Many poker players are overly timid before the flop, yet when they finally put money in the pot, they feel like they must win it. This usually leads to the player vastly overplaying marginal hands whereas in reality, they should be trying to control the size of the pot.
For example, you do not want to pile in your stack against most opponents with a hand such as A-K on a 7-4-2 board or Q-Q on a K-J-9 board. It is important to realize when you are somewhat likely to be beat. Even if you started with strong preflop cards, if your opponent is happy to put his stack in the pot, he usually has a premium hand that crushes much of your preflop starting range.
Do not fall into the trap of losing a ton of money simply because you started with strong cards. It is not uncommon to see an amateur player start with a premium hand such as A-A then lose his entire stack when the board comes 8-7-6-K-J by betting all three streets, perhaps all-in by the river. If your opponent is willing to call a substantial bet on all three betting rounds, you can be quite confident he can beat A-A, unless he is a calling station.
You must constantly assess your opponent’s range. While your cards are certainly important, your opponent’s cards are equally important. If you are only concerned with the two in your hand, you are certain to make costly mistakes that will make it essentially impossible for you to win at poker in the long run.