Maybe a different profession? Or maybe not.

Suppose you spent 30 years as missionary and found one convert. (And you weren't too happy with him) I hadn't known that about David Livingstone, who won only one man in his career as a medical missionary. Although that one man turned out to be a tremendously effective evangelist ...

To be fair, Livingstone wasn't working full-time at evangelism the whole time; he was also exploring. I wonder if he heard a little of what his disappointing protege accomplished; the simple online biographies don't seem to say.