Judas betrayed Christ, and on the same night Peter denied Jesus. While Judas did regret his decision--evidenced by his returning the silver--he despaired and committed suicide. Peter too regretted his decision, as he wept once the cock crowed. But he remained with the other apostles and disciples, maintained hope in the resurrection, and later had the opportunity to directly tell Christ not once but three times--to counter his three denials--that he loved Him. To me this is a powerful story of why we should not despair in the face of our sin but repent and remember Christ's love, forgiveness, and mercy.