Ive seen most prompts before. I know what pressing cancel or ok on each one does without thinking. And if I dont know what it does, I have to pause and figure out the consequence of each button.
And when I watch other people use computers, they will close things, and I ask them "what was that" they often respond "I dont know, I didnt ask for it, so I closed it." There seems to be a persuasive misunderstandig that dismissing a prompt will leave everything in its previous state, and that it cant make any changes.