Limits

It approaches, but never touches. It gets infinitely close, but never arrives. It is the definition of commitment issues.

And the ε-δ definition? "For every epsilon greater than zero..." stop. Just stop. If you have to use Greek letters to explain why you are close to something, you aren't close enough.

Limits are the gateway drug to Calculus. They take perfectly good, solid numbers and turn them into ghosts. Nothing is exact anymore, everything is just "approaching".