Dumbledore's depiction reminds the confessor in three worlds collide. He mentions that there are very few humans who need help to be more optimistic, and his experience leads him to see all the ways that things can go wrong, so makes him suited for being rational. Similarly with Dumbledore, his experiences have made him highly risk averse, often to good, but it does result in him being unwilling to change things. (As a contrast to the more reckless/innovative Harry).