?The Imam should be Infallible (inerrant-sinless) from all sins. Why + The Imam is appointed because the people can make a mistake. So there must be someone to protect them. But if that person were also likely to make mistake then he too will be in need of another Imam, leader or guide. Therefore it will require either continuity of such appointments which is impossible or, ultimately, such an Imam will have to be there who cannot err and then only will he be the Imam.