In Poker, on any given day, chances are that if you get a favorable run of cards, you will win, and if you get a bad run of cards, you will lose. People who don't understand Poker suffer from one of two misconceptions:

1. Poker is just gambling and there isn't much skill, or,
2. Poker is all about skill and cards really don't matter.

Cards matter a ton. When the betting goes down, the game is a matter of skill. But once the money goes in, the game is all luck, or more accurately, all probabilities. So obviously, it stands to reason that winning players maximize their expectation when probability is on their side, and minimize losses when it isn't.

This is a fancy way of saying that on any given day, a good player can lose and a bad player can win. BUT, given the same run of cards, a good player will always win more than the bad player with a favorable run of cards, and will always lose less than the bad player with an unfavorable run of cards. This is a lesson I have taken from countless trips to the cardroom. I've seen donkeys with stacks of chips so high they can barely see over them, and still leave with nothing, yet when they get in bad time and time again, constantly reloading, they complain about what a bad run of cards they've been having. A good player, by contrast, will not let a string of careless mistakes erode his winnings for the day.

A good player will probably win a little bit or break about even given an average run of cards, depending on his exact edge. With a bad run of cards, he will probably be a small loser, or occasionally a big loser on a given day. With a good run of cards, however, he will probably be one of the biggest winners in the game.

Contrast that with a bad player. Given an average run of cards, he will probably still lose, because his mistakes will outweigh his good luck. With a bad run of cards, he will be a big loser, because his mistakes are compounded by bad luck. However, given a good run of cards, the bad player can go anywhere from being a small winner to even a loser on the session, depending on the size and frequency of his mistakes. I have seen bad players scoop pot after pot, only to lose it all in a series of blunders (mostly in Limit), or in one enormous faux pas (mostly in No Limit).

So the real difference between winners and losers is that good players do what they can with what they have. Bad players either don't care what they get and play it off as chance, or delude themselves into thinking that cards don't matter.

There are a lot of other differences, but that's the one I think it most critical, especially in endeavors like Poker that require a long-run view of things.