How and why do you think that Assef'd experience in jail caused him to become a part of the Taliban?

Besides, he joined the Taliban not for money but because he felt it was his divine task. When he was in prison in the 1980s, there was a guard who beat one prisoner each night in order to terrorize the others. One night, when Assef had a terrible kidney stone, the guard decided to beat him. He was wailing in pain as the guard beat him until one kick to his side dislodged the kidney stone and made it pass so that he laughed through the rest of his beating. Assef believed it to be "a message from God." Years later, he found the same man injured on the battlefield and shot him in the genitals. Ever since, he had been "on a mission" to get rid of those he considered unworthy of living in Afghanistan.