You need to be able to anticipate people. That means you can forgive, but you should never forget. Why? Because the best predictor of what people will do in the future is what they did in the past. You can forgive and forget a thief, but your forgetfulness of his nature will not change his criminal tendencies. If someone stabs you in the back and you survive, God saved you. But if you turn your back to him again, and this time he successfully stabs you to death, you become an accomplice in your own murder.