People do not forget easily, but God says that He does not remember our sins. The omniscient God chooses to forgive and not to remember, and if the omnipotent God forgives us, then we should do the same.
In failing we bring disappointment, distrust and doubt. That is why Satan wants us to fail, but in Jesus we will find restoration, forgiveness, healing, self-realisation, power, strength and a future. In Him we will find the power to stand