For the uninitiated, blackjack is a card game commonly played at casinos. Most blackjack players try to employ basic strategy in order to minimize their losses, which are typically anywhere between .3-2% of each bet. Typically you can play 50 hands/hour and you need to bet at least $5/hand, so that means that if you were to play without any deviations from basic strategy, in the long run you would lose between $1.50/hr and $10/hr.
Basic strategy only takes the cards on the table into account. There are advanced strategies that take every card that has been played into account. For example, if a lot of small cards have been played, but very few large cards have been played, it follows that a lot of large cards and only a few small cards remain. Card counting is a technique that looks at the cards that have been played in order to predict the cards that haven’t been played yet, and this information can give the player an advantage.