A mix of fortune and ability. French call it “vingt-et-un”, and it’s originated from a play born some centuries ago. Someone confuse it with the english card game called “Black Jack”. Now online casino is the homeland of blackjack, roulette and slots.
But perhaps it could be only a matter of science, a fact of numbers. Because blackjack has an important element of player choice, players can reduce the casino advantage by playing optimally: the set of optimal plays is known as basic strategy. There are slight variations depending on the house rules and number of decks.
Basic strategy provides the player with the optimal play for any blackjack situation based on millions of hands played in the long run. In the short run, instead, as the cards are dealt from the deck, the remaining deck is no longer complete. By keeping track of the cards that have already been played, it is possible to know when the cards remaining in the deck are advantageous for the player.
Depending on the particular blackjack rules in a given casino, basic strategy reduces the house advantage to near zero with some single-deck games. Card counting, if done correctly, can give the player an advantage, typically ranging from 0 to 2% over the house.
In most US jurisdictions, card counting is considered as legal and is not cheating. However, most casinos have the right to ban players and card counting is frequently used as a good justification to ban a player.