Why does the zero give the house an edge in roulette?

Fritz asks

I keep hearing that the house will always win because there is zero. It rarely comes up so why does that give the house an advantage?

Its true its the zero that gives the house an edge. Even though it comes up rarely, its enough for it to give the casino the small edge it needs to beat the player in the long term.

Imagine playing with 37 chips and covering every number. What ever number it hits, you will get 36 chips back including your stake. You will lose one chip every spin. Thats what essentially happens over the course of the game. You might be able to walk away up once in a while but long term, the house edge will eventually cause you to lose.