Harry was a solid choice but few would have expected him to perform as well as president as he did.

At the time, it probably didn't seem like a great choice, but as things unfolded, it was brilliant. Henry Wallace was a disaster but there was no indication that Truman was anything special. He was ,as it turned out, just the man for the job. When he left office as president, he was considered the worst ever. That can happen when you do what seems right in your heart. Now, he seems like one of the best. Long term results matter!

Looking back at Franklin D. Roosevelt's choice of Senator Harry S Truman, it is easy to say that it was a great move. But in 1944, Truman was not Roosevelt's first choice. In fact, FDR could have cared less with the two mentioned names of James Byrnes and his then-current Veep, Henry Wallace. His personal choice, Associate Justice William Orville Douglas was not what the convention wanted, and FDR never really pused his name thereafter. So it played out that the former haberdasher (and crony of Missouri Democratic political boss Tom Pendergast) from Independence, Missouri ended up getting the nomination, albeit not to the  by the party leaders at the time. Whether people knew it or not at the time, 'Haberdasher Harry' would eventually become one of the most admired ever Presidents of the United States.

A prescient choice as it turned out. Roosevelt had to know, given the state of his health, that he was likely picking the next president and he went outside the party power brokers to pick this guy.

I don't suggest that Truman was a great president, but he was generally a good one.