How did Mendel arrive at his discoveries?

There are few historical records concerning Gregor Johann Mendel and his work, so theories abound concerning his motivation. These theories range from Fisher's view that Mendel was testing a fully formed previous theory of inheritance to Olby's view that Mendel was not interested in inheritance at all, whereas textbooks often state his motivation was to understand inheritance. In this Perspective, we review current ideas about how Mendel arrived at his discoveries and then discuss an alternative scenario based on recently discovered historical sources that support the suggestion that Mendel's fundamental research on the inheritance of traits emerged from an applied plant breeding program.