You walk into a food factory and you ask for a pizza. It comes out and you tell them that you wanted mushrooms, so they make another one. It arrives and you complain that it's square and not round, so they make another one. That one has no tomato sauce so you send it back again. Eventually you get the pizza you want.

I make my own pizza because I like doing it. And if I can't be bothered to make one, I'll just pick a ready made one off a menu from a pizza restaurant.