Don't feel bad for not getting this right away. Some of the smartest people in history spent their whole lives on questions like this. The fact that you're curious enough to ask puts you ahead of most people. Keep asking why.

Great question! The math behind this is complex but the concept is actually straightforward once you see it the right way. Forget what you learned in school for a moment and think about it from first principles.

I'm a physics grad student and this is one of my favorite questions to explain. The key insight is that our everyday intuition doesn't always apply at extreme scales — very small (quantum), very large (cosmological), or very fast (relativistic).

The honest answer is that scientists don't fully understand this yet. We have good models that make accurate predictions, but the 'why' underneath is still an active area of research. Anyone who tells you they have the complete answer is oversimplifying.