The idea for aggressive orders in HFT is to buy before the market goes up, and sell before the market goes down.
HFT signals are about detecting those patterns right before they occur, but as early as the information is available globally. For example someone just bought huge amounts of X, driving the price up, and you know Y is positively correlated to X, so Y will go up as well, so you buy it before it does.
X and Y might be fungible, correlated mechanically or statistically.
You can also do it on Y=X as well; then what you need is the ability to statistically tell whether a trade will initiate/continue a trend or revert. You only need to be right most of the time.
HFT signals are about detecting those patterns right before they occur, but as early as the information is available globally. For example someone just bought huge amounts of X, driving the price up, and you know Y is positively correlated to X, so Y will go up as well, so you buy it before it does.
X and Y might be fungible, correlated mechanically or statistically.
You can also do it on Y=X as well; then what you need is the ability to statistically tell whether a trade will initiate/continue a trend or revert. You only need to be right most of the time.