Even though the concept and maths are fairly simple, a lot of recreational Blackjack players fail to realise that taking Even Money is identical to making an Insurance bet.
When the dealer has an Ace, players have the option of making an Insurance bet. This wager wins when the dealer makes blackjack, and loses on any other non-picture card. Most players know this wager is not a very good one, with a house edge of around 8%.
When a player has Blackjack and the dealer has an Ace, players have the option of taking Even Money for their hand, instead of 3:2 if the dealer doesn't get blackjack or pushing if the dealer does get blackjack.
The two bets are actually identical. Taking Even Money is exactly like making an Insurance bet on your blackjack hand. Let's assume you could place an Insurance bet on your $100 blackjack hand. You'd place $50 on the Insurance line and the dealer does not get blackjack - he'll take your $50 and pay you $150 for your blackjack hand, for a net profit of $100 for you. If the dealer does get blackjack, you'll receive nothing for your blackjack hand, but you'll get paid $100 profit for your Insurance bet. If you take Even Money, you get $100 for your blackjack hand.
As you can see, if you take Even Money or Insurance, you end up with a $100 profit no matter what happens. However, both bets are bad wagers, as you'll end up with more in the long run if you never take the option to Insure or take Even Money. In the long run, the Dealer won't get blackjack enough to make either bet a good bet.
Taking Even Money and making Insurance bets are bad strategy and you should always decline these options when offered to you.