Also, "working hard" is pretty meaningless without context, especially if we're going to talk about regretting it.

For example, carving out some time at night for your side projects that might pay your rent one day vs. staying longer at work to get a leg up on imminent deadlines that were too aggressive vs. working hard to be Employee of the Month vs. working hard to learn programming.

It's great you think that, but the data I've seen nearly always says the opposite.