"A stupid person is a person who causes losses to another person or to a group of persons while himself deriving no gain and even possibly incurring losses."

Yeah, this lines up with my personal description of stupid: incapable of achieving one's own goals because of stubbornness, mean-spiritedness, pride, persistent misunderstanding, inability or unwillingness to learn. A danger to themself and others. Usually and unfortunately coupled with overconfidence.

This is stark contrast to being merely ignorant (lacking knowledge, naive or sheltered) and dumb (incapable of learning or grasping complex subjects).

Ignorance is generally fixable and with some capacity, dumbness too. But stupidity is a special kind of bad.

But, ummm, if nature abhors a vacuum? And all these things provide "opportunity" for improvement? Maybe the special bad is by design.