I asked my kids that question, and they couldn't really come up with an example. The dictionary isn't really any better. It may describe luck as "chance" or "fortune", and sometimes as a "force" that brings chance, but that's not really how we commonly use it, which is in the "prescriptive" sense. Consider the following:
- He sure is lucky!
- I've got a lot of luck, and all of it's bad.
- I wish I had your luck.
In common usage, "luck" is something you can have, and can transfer. Even though it's yours, it's certainly it's outside your control. You don't manipulate it with skill, logic, or experience. You don't earn luck. You're just "lucky" and good (or bad) things happen to you. Lucky you. Though it's described as a "force", it can't be one in the physical sense. Different people "have it" to different degrees.
This is a purely supernatural, superstitious, and primitive belief. We know that there is no magical pool of "stuff" that can just make "good things" happen around you. The more you think about it, the dumber you feel about ever having believed in it. It's just plain silly.
Current Liberal -- and particularly Socialist -- philosophies fueling class warfare rely heavily on this plainly silly concept. To them, your success or failure is not your own. To successful business owners, our President says, "You didn't build that." Criminals are told that their crimes are not their fault. But for luck their positions would be reversed. Their core thesis is that, good or bad, you didn't earn your fate; therefore you don't deserve it. And since you didn't earn anything you have, everything you have should be subject to re-distribution to those who deserve it equally... that is: not at all.
It's all just luck. And the more you think about it, the dumber you should feel for ever having believed it.