Poker players are required to think on many levels in order to master the game and take advantage of their opponents.
An example being that you are playing a certain way and trying to convince your opponent you have cards that you really don’t have. So you are 1 level of thinking above this player by playing into what they think you have. It may sound like a mouthful but the person who is at the highest level can usually come out on top. Of course it truly helps to be correct in your judgement of what your opponent is really thinking and doing.
Most people have problems of thinking they are good at poker when they are not so they fail on the most basic level.