Fermi was known for asking students and colleagues questions that seemed, at first, to require complex physics or information they did not have access to. On a road trip he once asked: How thick will dust pile up on the windshield of our car if we’re driving at 60 mph?

A precise answer wasn’t the point. His questions were exercises in approximation. You chain together a bunch of estimates you feel reasonably confident in, to arrive at an answer that gives you an order-of-magnitude sense of whatever phenomenon. You’d be surprised what you know!