Playing poker is a good reminder that it takes patience to earn rewards. One of the hardest parts is waiting for good hands. It's easy to get anxious and bet on low probability hands instead of waiting patiently.
Early in the game, it's ok to bet bigger than normal to gauge the reactions of other players on the table, but as the game progresses it's important to be thoughtful. Unfortunately, this means that winning can take hours. So unless you're willing to wait out the competition, you should be ready to part with your chips quickly.
Poker is a mental battle.
Like in real life, it's easiest to fold when the stakes are lowest. You may have a great hand, but it may still be prudent to fold. The best players differentiate themselves by keeping emotion out of these decisions.