Imagine you spent a long time drawing a beautiful picture or building a LEGO castle. You put a lot of energy into it. But then you go play something else, don't put it away properly, and someone steps on it, breaks it, or your toy disappears. So annoying, right?
The Bible says it's the same thing with grown-ups' effort. When we don't take care of what we've earned, a "stranger" comes and takes it away. That's why Mom and Dad work carefully and take care of what belongs to you!