Just don't exaggerate his stupidity. A 6 intelligence is dumb, but not incredibly so. An 8 wisdom is only slightly below average. People far too often forget that about 1 in 200 humans have a 3 intelligence. Nearly 10% of all humans have an intelligence score of 6 or below. He's not that dumb. His 8 wisdom is better than 25% of the human population. Heck, 1 in 50 even have a charisma as low as his, or even worse.
It gets old watching player and player again treat an 8 intelligence as functionally retarded. I've even seen players who think a 10 or an 11 is an excuse to play dumb and get their party into trouble with a series of ridiculously stupid actions.
D&D Statistics
Right...
But when you start stacking 2 or 3 low mental stats together, there is a certain "negative" synergy. A guy who is not only a bit slow- Int 7 or less, for argument's sake- but whose Wis is in the same range may routinely make bad decisions because he is unwise as well as slow.