Quote from illiquid:
The truth is, for the most part, all you see on level 2 and time & sales is designed to part you from your money (or stock) at exactly the wrong time. Sure once in a while you'll catch a runner and take a few hundred shares of a stock that never looks back.
But for about 90% of my trades (hint: I don't scalp), they are underwater if only temporarily within the next 0-60 secs. The larger the position you take relative to avg daily volume, the more likely this will be. What keeps you in the trade is conviction vs everything you see on your screen. The test may only be for a few short seconds, but 90% of the time they WILL test you.
What does this mean for you as a trader? You better know what you are doing, because the trades that are right and the trades that are dead wrong often look exactly the same (wrong) for some period of time. It's up to you and your experience to separate between the two.
True, the system is built to shake you out and take your stops, otherwise it will be an easy game, you buy low and sell high, that is where accepting small losses and money management come in.