They have to move up by responding to challenges, not too easy not too hard, until they paused at what they always think is the end of the road for all time instead of a momentary break in an endless upward spiral For me an intelligent woman is one who takes care and respects herself and her loved ones.
Don't confuse intelligence with overall knowledge of politics, philosophy or general cultural knowledge, also with college degrees...
And probably the most important reason you don't want a dullard for a wife is simply that dullards are far less capable of recognising the long term consequences of their actions.
That means your dumb-as-dog-shit wife is far more likely to start fucking the milk-man than your intelligent one (note that IQ has a strong negative correlation to selfishness as well).
That's when you pull down their pants and spank their bottom blue.