Blackjack is a game that involves both skill and luck. While luck plays a significant role in the cards you are dealt, skill comes into play in terms of knowing when to hit, stand, double down, or split.
While luck certainly does have a part to play in Blackjack, there is a lot of skill that goes into playing the game. How much skill or strategy you use depends on the time and effort you are willing to put into learning these skills. One such skill is card counting-not like by casinos but certainly not illegal.