Defining stupidity

I watched a documentary on stupidity.  It posed the question of "What is stupidity?" but never defined it, probably because it's too nebulous to define.

The best definition I can think of is this:

stupidity (n.)

1. To act in contradiction to reality, facts, and/or one's own interests

2. To deny and ignore reality and facts in pursuit of one's desires or ambitions

It's not a perfect catch-all, but it fairly well describes things most educated would call stupid:

• "daredevils" and other physically dangerous acts
• religion, creationism, climate change denial, political hypocrisy
• obsession and fanaticism (music, movies, sports, etc.)