Although a better example might be if you made a copy my car and used it. Because then I can use my car at the same time as you are using the copy.
How about this example using intellectual property instead…
You're broke and out on the streets. In despair and because you have nothing better to do, you write about your life and how you got to that point. Someone sees your finished work. He says it's really good and asks for a copy. You don't have one because you don't have any money. He gives you $10. You run off a copy and hand it over.
Wow, you just got $10 for something you created, minus the cost you paid to provide a copy. Over the next few days you start wondering if you could get $10 for another copy, maybe more. You could really use the money, and the prospect gives you something you haven't had in a long time…hope.
So with what you have left of the $10, you run off some copies, stand on the nearest corner and ask passersby if they're interested in buying your work.
Quite a few people stop and gush over your offering, but no, they're not interested in buying it because the guy who paid you $10 has already given them copies that he made, plus he's been giving private readings.
So you go back to your cardboard box in the alley with your hopes dashed and potential earnings up in smoke.
No harm, right?