When I was young, I owned a pair of rollerskates. But a few months later, a new kind of rollerskates came to the market: the rollerblades. Since I wanted a pair of rollerblades really badly, I convinced my mom that if I sold the old ones, I could buy the new ones (YAY!).
But, there was a caveat: My mom had to pre-approve of the price that I sold the old rollerskates before I got rid of them (and I naively thought that I could get rid of them for a couple of bucks…).