Basic blackjack strategy is essentially about making correct mathematical decisions. There is no need to actually do any math yourself, though, as the correct decisions have all been worked out and turned into a set of rules. These rules effectively tell you what to do based on the information available to you – which is the cards in your hand and the dealer’s up card.
The rules work because there are a fixed number of cards in the deck, and therefore a finite number of possible combinations that can be dealt. It is possible to mathematically determine which decision gives you the best chance of winning a hand in any given situation.
The odds are still against you in the long run, because of the house edge, but if you apply basic strategy, you will keep the casino’s advantage to a minimum.