Shimura's biography "Map of my life" is a fascinating read, especially on his tragic friendship with Taniyama which led to the Taniyama-Shimura conjecture.
He mentions in the Horizon "Fermat's Last Theorem" documentary that Taniyama was "not a careful person as a mathematician. He made a lot of mistakes, but he made mistakes in a good direction, so eventually he got [to] the right answer, and I tried to imitate him, but I found out that it is very difficult to make good mistakes." He says it with a wry grin.
I knew nothing about Taniyama until I read his Wikipedia article, which says he suffered from depression and committed suicide at age 31; and soon after the woman he was going to marry also committed suicide. https://en.m.wikipedia.org/wiki/Yutaka_Taniyama