Stupid, silly, dumb, foolish, fool, idiotic, imbecile, fatuous, daft, doltish, sappy, goofy, rattle-headed, nit-witted. I could go on and on with word describing (other) peoples lack of intelligence. Languages are usually full of these words. But people are not stupid!
They just have bad luck when they think!
People make mistakes, be forgiving. Ha de Gött!