Mistake #1: Not using basic strategy
The single biggest mistake blackjack players make is playing by gut feeling instead of mathematically optimal strategy. Basic strategy charts reduce the house edge from roughly 5% down to under 0.5%.
Mistake #2: Taking insurance
Insurance pays 2 to 1 when the dealer has blackjack, but the dealer holds a ten-value card less than a third of the time, so the bet carries a house edge of around 7%. Decline it.
Mistake #3: Playing 6:5 blackjack
Some casinos have shifted from the traditional 3:2 payout to 6:5. This seemingly small change increases the house edge by about 1.4%. Always look for 3:2 tables.
Mistake #4: Ignoring table rules
Not all blackjack tables are created equal. The number of decks, whether the dealer hits or stands on soft 17, and doubling restrictions all affect your odds significantly.
Mistake #5: Poor bankroll management
Even with perfect strategy, variance will test your bankroll. A good rule of thumb is to have at least 30-50 times your minimum bet as your session bankroll.