Large orders and market manipulation
"If you own a stake large enough to do that, you became regulated - under Section 13(d) of the 1934 Act and Regulation (in case of US stock) and you became regulated. Restricting you from ""shocking"" market. Another thing is that your broker will probably not allow you to execute order like that - directed MKT order for such volume. And market is deeper than anyone could measure - darkpools and HFTs passively waiting for opportunities like that."
I would say the most challenging fact for this assertion is that HFT firms operate with extremely limited capital bases. For a stock with say 10m shares ADV, even a very large and successful HFT strategy might use a position limit of no more than 5000 shares.  That is to say if you sum up and net the buys and sells for a stock across the day the HFT firm will never exceed 10,000 shares (2x position limits assuming it completely flipped) on a stock that trades 10,000,000 shares on a given day. The high volumes are attained through high turnover, the strategy might trade up to 500,000 shares (or 5% of the volume) attaining a 50x turnover.  But that brings me back to the original point. In the market microstructure literature market impact generally has been found to scale linearly or even sub-linearly for net volume executed.   If I alternate between thousands of 1 lot buy and sell orders, it would be very difficult for me to move the market because the market impact of every one of my buy orders roughly cancels the market impact of my almost exactly equal number of sell orders.   There might be a higher-order mechanism at work, but I'm genuinely curious what you think it might be. How could strategies that attain such small net positions have such out-sized impact on market direction? Market orders can be reasonably safe when dealing with stocks that are rather liquid and have quite low volatility. But it's important to note that you're trading a large degree of control over your buy / sell price for a small benefit in speed or complexity of entering an order. I always use limit orders as they help me guard against unexpected moves of the stock. Patience and attention to details are good qualities to have as an investor. Firstly what are you trading that you could lose more than you put in? If you are simply trading stocks you will not lose more than you put in, unless you are trading on margin. A limit order is basically that, a limit on the maximum price you want your buy order bought at or the minimum price you want your sell order sold at. If you can't be glued to the screen all day when you place a limit order, and the market moves the opposite way, you may miss out on your order being executed. Even if you can be in front of the screen all day, you then have to decide if you want to chase the market of miss out on your purchase or sale. For example, if a stock is trading at $10.10 and you put a limit buy order to buy 1000 shares at or below $10.00 and the price keeps moving up to $10.20, then $10.30 and then $10.50, until it closes the day at $11.00. You then have the choice during the day to miss out on buying the shares or to increase your limit order in order to buy at a higher price. Sometime if the stock is not very liquid, i.e. it does not trade very often and has low volume, the price may hit $10.00 and you may only have part of your order executed, say 500 out of your 1000 shares were bought. This may mean that you may have to increase the price of your remaining order or be happy with only buying 500 shares instead of 1000. The same can happen when you are selling (but in reverse obviously). With market order, however, you are placing a buy order to buy at the next bid price in the depth or a sell order to sell at the next offer price in the depth. See the market depth table below:  Note that this price depth table is taken before market open so it seems that the stock is somewhat illiquid with a large gap between the first and second prices in the buyers (bid) prices. When the market opened this gap is closed, as WBC is a major Australian bank and is quite liquid. (the table is for demonstration purposes only). If we pretend that the market was currently open and saw the current market depth for WBC as above, you could decide to place a limit sell order to sell 1000 shares at say $29.91. You would sell 100 shares straight away but your remaining 900 sell order will remain at the top of the Sellers list. If other Buyers come in at $29.91 you may get your whole sale completed, however, if no other Buyers place orders above $29.80 and other Sellers come into the market with sell orders below $29.91, your remaining order may never be executed. If instead you placed a market sell order you would immediately sell 100 shares at $29.91 and the remaining 900 shares at $29.80. (so you would be $99 or just over 0.3% worse off than if you were able to sell the full 1000 shares at $29.91). The question is how low would you have had to lower your limit order price if the price for WBC kept on falling and you had to sell that day? There are risks with whichever type of order you use. You need to determine what the purpose of your order is. Is it to get in or out of the market as soon as possible with the possibility of giving a little bit back to the market? Or is it to get the price you want no matter how long it takes you? That is you are willing to miss out on buying the shares (can miss out on a good buy if the price keeps rising for weeks or months or even years) or you are willing to miss out on selling them right now and can wait for the price to come back up to the price you were willing to sell at (where you may miss out on selling the shares at a good price and they keep on falling and you give back all your profits and more). Just before the onset of the GFC I sold some shares (which I had bought a few years earlier at $3.40) through a market order for $5.96. It had traded just above $6 a few days earlier, but if instead of a market order I had placed a limit order to sell at $6.00 or more I would have missed out on the sale. The price never went back up  to $6 or above, and the following week it started dropping very quickly. It is now trading at about $1.30 and has never gone back above $2.00 (5.5 years later). So to me placing a limit order in this case was very risky. "After learning about things that happened in the ""flash crash"" I always use limit orders. In an extremely rare instance if you place a market order when there is a some glitch, for example some large trader adds a zero at the end of their volume, you could get an awful price.  If I want to buy at the market price, I just set the limit about 1% above the market price. If I want to sell, I set the limit 1% below the market price. I should point out that your trade is not executed at the limit price. If your limit price on a buy order is higher than the lowest offer, you still get filled at the lowest offer. If before your order is submitted someone fills all offers up to your limit price, you will get your limit price. If someone, perhaps by accident, fills all orders up to twice your limit price, you won't end up making the purchase. I have executed many purchases this way and never been filled at my limit price." "Yes this is possible in the most liquid securities, but currently it would take several days to get filled in one contract at that amount There are also position size limits (set by the OCC and other Self Regulatory Organizations) that attempt to prevent people from cornering a market through the options market. (getting loads of contacts without effecting the price of the underlying asset, exercising those contracts and suddenly owning a huge stake of the asset and nobody saw it coming - although this is still VERY VERY possible) So for your example of an option of $1.00 per contract, then the position size limits would have prevented 100 million of those being opened (by one person/account that is). Realistically, you would spread out your orders amongst several options strike prices and expiration dates. Stock Indexes are some very liquid examples, so for the Standard & Poors you can open options contracts on the SPY ETF, as well as the S&P 500 futures, as well as many other S&P 500 products that only trade options and do not have the ability to be traded as the underlying shares. And there is also the saying ""liquidity begets liquidity"", meaning that because you are making the market more liquid, other large market participants will also see the liquidity and want to participate, where they previously thought it was too illiquid and impossible to close a large position quickly" Like in the US, more flexibility is extended to hidden orders. Australia has taken an aggressive approach to hidden orders in the direction of lower ticks. Aussies have a rich financial that evolved differently than the Dutch custom more familiarly known in the UK and US. They, like Chicago evolved out of commodities trade rather than trade.  When commodities are worth nearly nothing per unit, larger precision comes naturally. For the Dutch, it was the opposite.  A single ship would trade in 1/64 share or for the largest vessels, 1/128 share.  Here, there's no point to high precision.  New York, founded by the Dutch specialized in logistics just the same.   To a man with a hammer, everything looks like a nail, so both Chicago, Australia, and other financial systems built by commodities rather than trade have extended the higher precision logic to everything else, and pricing is fantastic. It should not be a surprise why Australia has taken a lead in pushing infinite precision. You can execute block trades on the options market and get exercised for shares to create a very large position in Energy Transfer Partners LP without moving the stock market. You can then place limit sell orders, after selling directly into the market and keep an overhang of low priced shares (the technical analysis traders won't know what you specifically are doing, and will call this 'resistance'). If you hit nice even numbers (multiples of 5, multiples of 10) with your sell orders, you can exacerbate selling as many market participants will have their own stop loss orders at those numbers, causing other people to sell at lower and lower prices automatically, and simultaneously keep your massive ask in effect. If your position is bigger than the demand then you can keep a stock lower. The secondary market doesn't inherently affect a company in any way. But many companies have borrowed against the price of their shares, and if you get the share price low enough they can get suddenly margin called and be unable to service their existing debt. You will also lose a lot of money doing this, so you can also buy puts along the way or attempt to execute a collar to lower your own losses. The collar strategy is nice because it is unlikely that other traders and analysts will notice what you are doing, since there are calls, puts and share orders involved in creating it. One person may notice the block trade for the calls initially, but nobody will notice it is part of a larger strategy with multiple legs. With the share position, you may also be able to vote on some things, but that solely depends on the conditions of the shares. From every article I've encountered, the chicken and egg aspect suggests that IV is produced by looking at options pricing, and calculating the IV from that.  The implication is that whatever is known at that time is included in the price. And that when you see a particular option trade an unusual number of contracts at a given price, the implication is that someone thinks they know something that's not already priced in, i.e. that the current price is not accurate, they can profit on the future event.