For example: The market is set to open lower. Oil is trading down too. I see one of my stocks in the oil/energy sector looks to be a good sell off the open. When the market opens, I get short the stock (opening print), and the setup appears to be a good one (based on my experience). But when I get filled and then evaluate the situation, I can tell that what the stock would "normally do" in this situation, its not doing. Where the trade may normally net me 30-60 cents or more, it either nets me less than 20, or worse, a loss. I can tell right away based on liquidity that I have to be cautious until I see (if it happens at all) that the conditions get better. Alot of it for me is touch and feel. The details are key, knowing your stocks and knowing what normally drives them a certain distance. Also, the S&P futures are extremely important to me in determining the likelylihood of high probability trades vrs whipsaws and chop. If I see too many moving averages in a tight range on my S&P 5 min chart, I know to tone it down until we break one way or the other. The more I think about it, this topic is really hard to fully explain because there are so many variables that lead to the quick conclusion of whether to be more agressive with my trades or to be more defensive and more quick to take profits. This goes back to my first post on this thread in which I said that the difference, I think, comes down to experience/trader intuition.