Your online blackjack strategy chart may not indicate this, but it is always a mistake to take insurance. Insurance is offered when the dealer has an ace showing. The player has the option to take insurance by putting up a bet equal to half the original wager.
If the player takes insurance, the dealer checks for blackjack. If he has it, he wins the hand, but the player gets 2-to-1 on the blackjack bet, breaking even.
If the dealer does not have it, the player loses the insurance bet and play proceeds normally. If a player who is dealt blackjack takes insurance, he gets 1-to-1 on his money rather than the normal 3-to-2, regardless of the outcome of the hand.
The dealer will have blackjack more often than we would like. However, more often than not, he will not have blackjack, so this is a bad bet whether the player has blackjack or not. - http://www.casinosuccess.org/
