Here is a classic no-limit situation. You call a raise out of the big blind. You then flop a flush draw and eventually make a non-nut flush. But your opponent comes alive on the river, and you have to decide whether to fold, call, or reraise against a big bet.
In these situations you’ll have plenty to think about — all the bet sizes, which hands your opponent would have checked or bet on which streets, how your opponent perceives you, and so on. Advanced poker requires the careful deduction and combination of these facts. An extra 10 or 20 hand combinations in a betting or checking range on the flop can make a big difference when it comes to figuring out what your opponent can have on the river.