What is the principle of forming an arbitrage strategy?
"Arbitrage is basically taking advantage of a difference in price.  Generally extending to ""in different places for the same thing"". A monetary version would be interlisted stocks, that is stocks in companies that are on both the NYSE/Nasdaq and Toronto stock exchanges.  If somebody comes along and buys a large number of shares in Toronto, that will tend to make the price go up - standard supply and demand. But if someone else can buy shares instead in NY, and then sell them in Toronto where the first person is buying up shares, where the price is higher, they the the arbitrageur (second person) can make pretty easy money. By its very nature, this tends to bring the prices back in line, as NY will then go up and Toronto will then go down (ignoring FX rates and the like for ease of explanation). The same can work for physical goods, although it does tend to get more complex with taxes, duties, and the like." Well, arbitrage is a simple mean reversion strategy which states that any two similar commodity with some price difference (usually not much)  will converge. So either you can bet on difference in prices in different exchanges or also you can bet on difference in futures value.  For example if current price of stock is 14$ and if futures price is 10$.  Then you can buy one futures contract and short one stock at the market price. This would lock in a profit of 4$ per share.
"You are right, if by ""a lot of time"" you mean a lot of occasions lasting a few milliseconds each. This is one of the oldest arbitrages in the book, and there's plenty of people constantly on the lookout for such situations, hence they are rare and don't last very long. Most of the time the relationship is satisfied to within the accuracy set by the bid-ask spread. What you write as an equality should actually be a set of inequalities.  Continuing with your example, suppose 1 GBP ~ 2 USD, where the market price to buy GBP (the offer) is $2.01 and to sell GBP (the bid) is $1.99.  Suppose further that 1 USD ~ 2 EUR, and the market price to buy USD is EUR2.01 and to sell USD is EUR1.99.  Then converting your GBP to EUR in this way requires selling for USD (receive $1.99), then sell the USD for EUR (receive EUR3.9601).  Going the other way, converting EUR to GBP, it will cost you EUR4.0401 to buy 1 GBP.  Hence, so long as the posted prices for direct conversion are within these bounds, there is no arbitrage." "As you say, the currency carry trade shouldn't work.  The deluge of new cash into a high-interest currency should result in falling exchange rates.  A November 2009 paper by Òscar Jordà and Alan Taylor of the University of California, Davis, may be offer one approach which is more stable.  According to The Economist: They find that a refined carry-trade   strategy—one that incorporates a   measure of long-term value—produces   more consistent profits and is less   prone to huge losses than one that   targets the highest yield. However, exchange rates, central bank interest rates, as well as money supply are all political as well as economic constructs.  An economic driver for arbitrage may be offset by political will (such as US quantative easing) or even social malaise (Japanese continual low inward investment). I wouldn't go so far as calling the carry trade ""free money"" - currencies have proven far too unstable for that - but state interference in markets tends to be clearly telegraphed and a trader with nerves of steel may take advantage of it." If you define dollar cost cost averaging as investing a specific dollar amount over a certain fixed time frame then it does not work statistically better than any other strategy for getting that money in the market.  (IE Aunt Ruth wants to invest $60,000 in the stock market and does it $5000 a month for a year.) It will work better on some markets and worse on others, but on average it won't be any better. Dollar cost averaging of this form is effectively a bet that gains will occur at the end of the time period rather than the beginning, sometimes this bet will pay off, other times it won't. A regular investment contribution of what you can afford over an indefinite time period (IE 401k contribution) is NOT Dollar Cost Averaging but it is an effective investment strategy. with the semi-strong form of the Efficient Market Hypothesis expected dividends are priced into the options and security already. If you are able to locate such an arbitrage opportunity then you should take it, but I suspect it will be more more difficult than you think. Remember that many dividends require you to have been a shareholder by a certain date prior to the dividend occurring. "There are two umbrellas in investing: active management and passive management. Passive management is based on the idea ""you can't beat the market."" Passive investors believe in the efficient markets hypothesis: ""the market interprets all information about an asset, so price is equal to underlying value"". Another idea in this field is that there's a minimum risk associated with any given return. You can't increase your expected return without assuming more risk. To see it graphically:   As expected return goes up, so does risk. If we stat with a portfolio of 100 bonds, then remove 30 bonds and add 30 stocks, we'll have a portfolio that's 70% bonds/30% stocks. Turns out that this makes expected return increase and lower risk because of diversification. Markowitz showed that you could reduce the overall portfolio risk by adding a riskier, but uncorrelated, asset! Basically, if your entire portfolio is US stocks, then you'll lose money whenever US stocks fall. But, if you have half US stocks, quarter US bonds, and quarter European stocks, then even if the US market tanks, half your portfolio will be unaffected (theoretically). Adding different types of uncorrelated assets can reduce risk and increase returns.  Let's tie this all together. We should get a variety of stocks to reduce our risk, and we can't beat the market by security selection. Ideally, we ought to buy nearly every stock in the market so that  So what's our solution? Why, the exchange traded fund (ETF) of course! An ETF is basically a bunch of stocks that trade as a single ticker symbol. For example, consider the SPDR S&P 500 (SPY). You can purchase a unit of ""SPY"" and it will move up/down proportional to the S&P 500. This gives us diversification among stocks, to prevent any significant downside while limiting our upside. How do we diversify across asset classes? Luckily, we can purchase ETF's for almost anything: Gold ETF's (commodities), US bond ETF's (domestic bonds), International stock ETFs, Intl. bonds ETFs, etc. So, we can buy ETF's to give us exposure to various asset classes, thus diversifying among asset classes and within each asset class. Determining what % of our portfolio to put in any given asset class is known as asset allocation and some people say up to 90% of portfolio returns can be determined by asset allocation.  That pretty much sums up passive management. The idea is to buy ETFs across asset classes and just leave them. You can readjust your portfolio holdings periodically, but otherwise there is no rapid trading. Now the other umbrella is active management. The unifying idea is that you can generate superior returns by stock selection. Active investors reject the idea of efficient markets.  A classic and time proven strategy is value investing. After the collapse of 07/08, bank stocks greatly fell, but all the other stocks fell with them. Some stocks worth $100 were selling for $50. Value investors quickly snapped up these stocks because they had a margin of safety. Even if the stock didn't go back to 100, it could go up to $80 or $90 eventually, and investors profit. The main ideas in value investing are: have a big margin of safety, look at a company's fundamentals (earnings, book value, etc), and see if it promises adequate return. Coke has tremendous earnings and it's a great company, but it's so large that you're never going to make 20% profits on it annually, because it just can't grow that fast. Another field of active investing is technical analysis. As opposed to the ""fundamental analysis"" of value investing, technical analysis involves looking at charts for patterns, and looking at stock history to determine future paths. Things like resistance points and trend lines also play a role. Technical analysts believe that stocks are just ticker symbols and that you can use guidelines to predict where they're headed.  Another type of active investing is day trading. This basically involves buying and selling stocks every hour or every minute or just at a rapid pace. Day traders don't hold onto investments for very long, and are always trying to predict the market in the short term and take advantage of it. Many individual investors are also day traders.  The other question is, how do you choose a strategy? The short answer is: pick whatever works for you. The long answer is: Day trading and technical analysis is a lot of luck. If there are consistent systems for trading , then people are keeping them secret, because there is no book that you can read and become a consistent trader. High frequency trading (HFT) is an area where people basically mint money, but it s more technology and less actual investing, and would not be categorized as day trading.  Benjamin Graham once said: In the short run, the market is a voting machine but in the long run it is a weighing machine. Value investing will work because there's evidence for it throughout history, but you need a certain temperament for it and most people don't have that. Furthermore, it takes a lot of time to adequately study stocks, and people with day jobs can't devote that kind of time. So there you have it. This is my opinion and by no means definitive, but I hope you have a starting point to continue your study. I included the theory in the beginning because there are too many monkeys on CNBC and the news who just don't understand fundamental economics and finance, and there's no sense in applying a theory until you can understand why it works and when it doesn't." Conglomerates don't work. We've seem thay countless times in countless periods in countless places in history... A focused company will always outperform an unfocused company in the long run...     Grocery stores trade at tiny multiples. Tech firms at massive multiples. The instant you buy a 3x EBITDA when you're trading at 15x EBITDA, you've increased the market value of the acquired firm by 5x... If you aren't familiar with Norbert's Gambit, it's worth looking at. This is a mechanism using a Canadian brokerage account to simultaneously execute one stock trade in CAD and one in USD. The link I provided claims that it only starts potentially making sense somewhere in the 10,000+ range. It seems to be that your main point is this: No matter what, my chances cannot be worse than random and if my trading system has an edge that is greater than the percentage of the transaction that is transaction cost, then I am probabilistically likely to make a profit? In general, yes, that is true, but... Consider this very bad strategy: Buy one share of stock and sell it one minute later, and repeat this every minute of the day. Obviously you would bleed your account dry with fees. However, even this horrible strategy still meets your criteria because: if this bad strategy had an edge beyond the transaction fees you would likely still make a profit. In other words, your conclusion reduces to an uninteresting statement: If there were no transactions fees, then if your trading system has an edge then you will likely make a profit. Sorry to be the bearer of bad news, but IMHO, that statement, and others made in the question are just obvious things stated in convoluted ways. I don't want to discourage you from thinking about these things though. I personally really enjoy these type of thought experiments. I just feel you missed the mark on this one...