The joy of wisdom is transitory. I am foolish enough to consider myself wise, but one bad day or gaping head wound could bring that to an end, and I would be reduces to a snarling beast or drooling idiot, or some idiotic snarling beast that drools a lot. If I escape those horrible possibilities, then there is the spectre of death, which would wipe all the wisdom away. If I wasn't so wise that would make me sad.