# Why does friction occur? [duplicate]

I'm pretty sure this is a rather stupid question but I just cannot wrap my mind around the reasoning behind friction.

Now, an obvious explanation would be that since all surfaces are inherently rough, the abnormalities sort of interfere with and obstruct each other, causing friction. But, as it turns out, friction is not a product of Newton's third law, so what is the fundamental force that causes opposing relative motion at a fundamental level?