I think one of the most important skills necessary to be a good poker player is being able to learn fast and have a good memory. Everyone talks about the stats/game theory aspect of poker which is important, but I think what I'm about to talk about is even more important.

For example: Say there is a $2405 pot and someone bets $1200 on the turn with $5200 eff stacks behind. You are contemplating between folding, going all-in or just calling. Determining the mathematically correct play only involves some advanced algebra. Ie. your EV when folding is 0. Your EV when calling is a combination of how often you hit, how often you get paid off, how often you bluff successfully later on, etc.

The unknown variable in this equation however is the percentage of time your opponent will act a certain way or have certain cards. Being able to estimate this percentage accurately is one of the most important skills great poker players have. It's not just hand reading. It's more than that. It's also determing how often a bluff will work (metagame aside), how often you'll get paid off, and many other things as well. But it can be grouped into things that being a faster learner with a good memory will be able to do very well.

No one actually works out the equation while they're playing. It's sort of a "feel" type thing based on past hands not only against the particular opponent, but against similar opponents as well if the opponent is an unknown. One of the most valuable tools online poker offers is it lets you see mucked cards after the hand is over. This is incredibly useful for the reasons I just wrote about. It probably speeds up your progress as a poker player by a factor of 10.