Matthew 26:33

Peter answered] 'He ought rather to have besought Christ, and begged for aid (against the coming temptation). But he sinned in three ways at once: (1) in contradicting the Prophet and the Christ, (2) in placing himself above the rest, (3) in trusting in himself alone, and not in the help of God. Wherefore also he was permitted to fall, that he might be humbled, and might learn not to trust too much in himself, and that others also might learn the same. Also he was allowed to fall that he might learn to love more. For he to whom more is forgiven, loves more '(Euthymius).