Also a great way to distinguish good programmers from bad. If they can't explain a phenomenon beyond "when I do <x> it works/breaks/quacks like a duck" and are

Also a great way to distinguish good programmers from bad. If they can't explain a phenomenon beyond "when I do <x> it works/breaks/quacks like a duck" and are satisfied with that level of understanding, that's a massive red-flag. This is a very efficient way of picking out even the young guys & gals who will end up being good engineers.