Could ignoring sunk costs be used to make an investment look more attractive when it's really not?
I'm not sure that you're considering all the options.   So you may not subtract $X from B, but you do compare NPV(B) to $Y.   Also, remember that we're not trying to figure out the return on B.  We're trying to figure out what to do next.  In terms of planning, the sunk cost is irrelevant.  But in terms of calculating return, A was a turkey.  And to calculate the return, we would include $X in our costs for B.  And for the second option, we'd subtract $X from $Y (may be negative).   Sunk costs are irrelevant to planning, but they are very relevant to retrospective analysis.  Please don't confuse the two.  When looking back, part of the cost for B will be that $X.  But in the middle, after paying $X and before starting B, the $X is gone.  You only have the building and have to make your decision based on the options you have at that moment.   You will sometimes hear $Y called the opportunity cost of B.  You could sell out for $Y or you could do B.  You should only do B if it is worth more than $Y.   The sunk cost fallacy would be comparing B to $X.  Assuming $Y is less than $X, this would make you not do B when it is your best path forward from that moment.  I.e. $Y < NPV(B) < $X means that you should do the project.  You will lose money (apparently that's a foregone conclusion), but you will lose less money than if you just sold out.   You should also do B if $Y < $X < NPV(B) or $X < $Y < NPV(B).  In general, you should do B any time $Y < NPV(B).  The only time you should not do B is if NPV(B) < $Y.  If they are exactly equal, then it doesn't matter financially whether you do B or not.
"If you are already invested in a particular stock, I like JoeTaxpayer's answer. Think about it as if you are re-buying the stocks you own every day you decide to keep them and don't set emotional anchor points about what you paid for them or what they might be worth tomorrow. These lead to two major logical fallacies that investor's commonly fall prey to, Loss Aversion and Sunk Cost, both of which can be bad for your portfolio in the long run. To avert these natural tendencies, I suggest having a game plan before you purchase a stock based on on your investment goals for that stock. For example a combination of one or more of the following: I'm investing for the long term and I expect this stock to appreciate and will hold it until (specific event/time) at which point I will (sell it all/sell it gradually over a fixed time period) right around the time I need the money. I'm going to bail on this stock if it falls more than X % from my purchase price. I'm going to cash out (all/half/some) of this investment if it gains more than x % from my purchase price to lock in my returns. The important thing is to arrive at a strategy before you are invested and are likely to be more emotional than rational.  Otherwise, it can be very hard to sell a ""hot"" stock that has suddenly jumped in price 25% because ""it has momentum"" (gambler's fallacy). Conversely it can be hard to sell a stock when it drops by 25% because ""I know it will bounce back eventually"" (Sunk Cost/Loss Aversion Fallacy).  Also, remember that there is opportunity cost from sticking with a losing investment because your brain is saying ""I really haven't lost money until I give up and sell it."" When logically you should be thinking, ""If I move my money to a more promising investment I could get a better return than I am likely to on what I'm holding.""" You are neglecting a few very important things around real estate transactions in Belgium So in the end a 300K building may cost you more than 340K, let's take some unexpected costs into account and use 350K for remainder of calculation. Even worse if it's newly built (which I doubt) the first percentage is 21% (VAT) instead of 10%. All these costs can be checked on the useful site www.hoeveelkostmijnhuis.be Now, aside from that most banks will and actually have to demand you pay part of all this yourself. So you can't do 5*60K (or 5*70K now). Mostly banks will only finance up to about 90% of the value of the building, so 90% of 300K, which is 270K (5*54K), the other 80K (5*16K) you have to pay yourselves. But it could be the bank goes as low as 80%. Another part to complicate the loan is how much you can pay a month. Since the mortgage crisis they're very strict on this. There are lots of banks that will not allow you to make monthly payments of more than 33% of your monthly income when you are going to live there. This is a nuisance even when buying one house, you want to buy 2. Odds seem low they'll accept high monthly payments because you either need an additional loan or need to pay rent, so don't count on a 5y deal. Now this is all based on a single loan, it will probably be a bit different with multiple loans. However, it is unlikely any bank will accept this, even if all loans are with the same bank. You need to consider the basics of a real-estate loan: A bank trusts you can pay it off and if not they can seize the real-estate hoping to regain their initial investment. It's very hard to seize a complete asset if only one out of 5 loan-takers defected. You could  maybe do this with another less restrictive/higher risk type of loan but rates will be a lot higher (think 5-6% instead of 1.5%). And don't underestimate the running costs: for that price and 5 rooms in that city you're likely looking at an older building. Expect lots of cost for maintenance and keeping the building according to code. Also expect costs for repairs (you rent to students...). You'll also have to pay quite a bit of money on insurances and of course on real estate taxes (which are average in Ghent). Also factor in that currently there is not a housing shortage for Ghent students so you might not always have a guaranteed occupation. Also take into account responsibility: if a fire breaks out or the house collapses or a gas leak occurs, you might be sued. It doesn't matter if you're at fault, it's costly and a big nuisance. Simply because you didn't think of any of this: don't do this. It's better to invest in real estate funds. But if you still think you can do better then all the landlords Ghent is riddled with, don't do it as a personal investment. Create a BVBA, put some investment in here (like 10-20K each), approach a bank with a serious business plan to get the rest of the money as a loan (towards a single entity - your BVBA) and get things going. When the money comes in you can either give yourselves a salary or pay out profits on the shares. You may be confused about how rich you can become because we as a nation tend to overestimate the profitability of real estate. It's really not that much better than other investments (otherwise everybody would only invest in real estate funds). There are a few things that skew our vision however: "The response to this question will be different depending which of the investment philosophies you are using.  Value investors look at the situation the company is in and try to determine what the company is worth and what it will be worth in the future. Then they look at the current stock price and decide whether or not the stock is priced at a good deal or not. If the stock price is priced lower than they believe the company is worth, they would want to buy stock, and if the price rises above what they believe to be the true value, they would sell. These types of investors are not looking at the history or trend of what the price has done in the past, only what the current price is and where they believe the price should be in the future.  Technical analysis investors do something different. It is their belief that as stock prices go up and down, they generally follow patterns. By looking at a chart of what a stock price has been in the past, they try to predict where it is headed, and buy or sell based on that prediction.  In general, value investors are longer-term investors, and technical analysis investors are short-term investors.  The advice you are considering makes a lot of sense if you are using technical analysis. If you have a stock that is trending down, your strategy probably tells you to sell; buying more in the hopes of turning things around would be seen as a mistake. It is like the gambler in Vegas who keeps playing a game he is losing, hoping that his luck changes.  However, for the value investor, the historical price of a stock, and even the amount you currently have gained or lost in the stock, are essentially ignored. All that matters is whether or not the stock price is above or below the true value determined by the investor. For him, if the stock price falls and he believes the company still has a high value, it could be a signal to buy more. The above advice doesn't really apply for them.  Many investors don't follow either of these strategies. They believe that it is too difficult and risky to try to predict the future price of an individual stock. Instead, they invest in many companies all at once using index mutual funds, believing that the stock market as a whole always heads up over a long time frame. Those investors don't care at all if the prices of stock are going up or down. They simply keep investing each month, and hold until they have another use for the money. The above advice isn't useful for them at all.  No matter which kind of investing you are doing, the most important thing is to pick a strategy you believe in and follow the plan without emotion. Emotions can cause investors to make mistakes and start buying when their strategy tells them to sell.  Instead of trying to follow fortune cookie advice like ""Don't throw good money after bad,"" choose an investment strategy, make a plan, test it, and follow it, cautiously (after all, it may be a bad plan). For what it is worth, I am the third type of investor listed above. I don't buy individual stocks, and I don't look at the stock prices when investing more each month. Your description of your own strategy as ""buy and hold"" suggests you might prefer the same approach." "A ""sunk cost"" is a cost that you have already incurred, and won't get back. The ""sunk cost fallacy,"" as you described, is when you make a bad decision based on your sunk cost.  When you identify a sunk cost, you realize that the money has been spent, and the decision is irreversible.  Future decisions should not take this cost into account.  When you commit the ""sunk cost fallacy,"" you are keeping something that is bad simply because you spent a lot of money on it.  You are failing to identify the correct current value of something based on its high cost to you in the past. The other fallacy you describe, the opposite of the sunk cost fallacy, is when you get rid of something that is good simply because you spent little on it.  As before, you are also failing to correctly identify the correct current value of something, but in this case, you are assigning too little a value based on the low cost in the past.  You could call this a type of ""opportunity cost,"" a loss of future benefits due to a mistake made today.  It seems reasonable to describe this type of fallacy as an ""opportunity cost fallacy.""" No. That's the point of a passive strategy: you maintain a more or less constant mix of assets and don't try to figure out what's going to move where. You could pay off a portion of the debt and your minimum payments should also go down proportionately.  Your investment managers may be able to continue making returns in the markets in a sideways and a bear market. So you have 24k contributing to your net worth, and ~50k giving you a negative net worth. At best, you can bring this down to a negative 25k net worth, or you can start and keep using some of the gains from your investment account to supplement your credit payments (along with your income). This is based on chance that your investment managers can continue making gains, compared to paying down 24k and having possibly zero liquid savings now, but having more of your salary to start saving and make the lowered minimum payments, assuming you don't borrow more. Those are the options I've thought of, I don't see either option being necessarily quicker than the other. "leverage amplifies gains and losses, when returns are positive leverage makes them more positive, but when returns are negative leverage makes them more negative. since most investments have a positive return in ""the long run"", leverage is generally considered a good idea for long term illiquid investments like real estate.  that said, to quote keynes: in the long run we are all dead. in the case of real estate specifically, negative returns generally happen when house prices drop. assuming you have no intention of ever selling the properties, you can still end up with negative returns if rents fall, mortgage rates increase or tax rates rise (all of which tend to correlate with falling property values). also, if cash flow becomes negative, you may be forced to sell during a down market, thereby amplifying the loss.  besides loss scenarios, leverage can turn a small gain into a loss because leverage has a price (interest) that is subtracted from any amplified gains (and added to any amplified losses). to give a specific example: if you realize a 0.1% gain on x$ when unleveraged, you could end up with a 17% loss if leveraged 90% at 2% interest. (gains-interest)/investment=(0.001*x-0.02*0.9*x)/(x/10)=-0.017*10=-0.17=17% loss one reason leveraged investments are popular (particularly with real estate), is that the investor can file bankruptcy to ""erase"" a large negative net worth.  this means the down side of a leveraged investment is limited for the highly leveraged investor. this leads to a ""get rich or start over"" mentality common among the self-made millionaire (and failed entrepreneurs).  unfortunately, this dynamic also leads to serious problems for the banking sector in the event of a large nation-wide devaluation of real estate prices." "I assume by that you mean gradually buying the same mix of funds over time.  If that's the case, there is no rational reason to do this.   Dollar-cost averaging is an artifact of the way most people fund their 401(k).  I would not consider it a viable ""strategy"".  (Neither does Wikipedia)  Let's say you have $100,000 that you add $10,000 at a time.  When you add money, one of three things can happen: Since you can't predict the future, there's no mathematical justification for buying in segments.  There's just as much chance that your funds will be worth more or less, so on average it should make little to no difference.   In fact, given the time value of money there is a slight  advantage to investing it all now so you can capture any future returns.  You can always rebalance later to capture gains on some funds and purchase funds that are down to (hopefully) catch them on a rebound."