[SBR Drew]

Expected value is the basic math that is the foundation of all advantage gambling. Until you understand what it is and how it works, you’re going to have a hard time beating the casinos. The good news is that you’re going to learn everything you need to know about expected value in this section.
The first time I read about expected value I didn’t understand it. It was in a book by David Sklansky, and it sounded like something important, but it was a bit difficult to wrap my head around. Eventually, I started to understand it and went back over the basics many times.
Expected Value, Explained

Every decision you make as a gambler has an average value over the long run. If you make the same decision or play hundreds or thousands of times, there’s an average value. In the short term, usually just a single decision or play, the value is either just a win or a loss.
But if you average the value over many times, you can determine if a play is profitable or unprofitable on average. Advantage gamblers look for profitable expected value and do everything they can to make these bets. This is called positive expectation.
If you make positive expectation wagers more often than negative expectation ones, you win more than you lose. This is why expected value is the most important mathematical concept for advantage gamblers.

[vivaporto]

Those who truly understand expected value will not play casino games (with the exception of sports betting and live poker) because you cannot use skill to beat a negative ev of casino games in the long run. Casino games are just meant for entertainment and if you win good but if you play to make money, you will lose and lose and lose.

Sports betting and poker are the two events where you can use skill to come out on top. This is a very good read about EV http://www.bettingresource.com/expected-value.html