Casinos and online casinos love to perpetuate the idea that blackjack is the one casino game in which the house can be beat. They will even admit that you need a blackjack strategy to beat the house. And they are more than willing to perpetuate the myth that blackjack strategy is the key to beating the house.
And they would be lying to you.
It is true that basic strategy is a major tool against the house in blackjack, but it will not beat the house on its own. Playing according to basic strategy can lower the house edge to 0.5%. But players must play it perfectly, otherwise that 0.5% is not achievable.
Even if you are playing perfect basic strategy there will be times that you lose a round. This is because you only have a 48% chance of winning (ignoring pushes) in blackjack, even if you are using basic strategy. Think about it