Stupidity combined with agency (when others decide for you), are the source of most problems that can be solved but are not.
Agency is very central in modern life. So many things are managed by others (add government....), and other things are honestly beyond our ability to do alone (doctors)
Stupidity alone can be solved via the help of others. we do not know the physics of car engine, the intricacies of computers etc. Yet we get them done by others.
But agency means that those others can take advantage of our stupidity. The mortgage salesmen knows we cannot pay such a huge mortgage yet sells it, the real estate guy persuades us for a bigger house etc.
Without stupidity, agency would not be so pernicious, because we would spot it much sooner. and will be harder to fool.
Yet combined they are the source of most public problems.