If by physics you mean the class, then I wouldn't exactly call it exciting. It's been years and I don't find myself doing arbitrary physics experiments just for fun. If you're talking about something else (like physics engines for a game), then you should clarify.

Legos? They didn't have any staying power. It was amusing at times to snap them together, but that was years and years ago when I was a kid. I sure don't own any now. It was fun to help a friend make some pixel art with it a couple of years ago, but all alone it would have been boring.

It seems we may have stumbled across a fundamental difference here.

Not physics the class, just the "how things work" aspect. I guess you could file chemistry under that as well.

I didn't actually find physics in college very interesting, because it seemed more focused on memorization. But I find reading Stephen Hawking books pretty interesting, even though I cannot think of many practical applications of his theories to my daily life, hobbies, or job. I like to understand how things work, and I do find "how things work" to be fun to play with. Materials and chemicals are pretty interesting to play with, as well.

Perhaps it is a fundamental difference. To me, building and understanding things (whether they're computational, mechanical, chemical, whatever) is interesting, but their ends aren't necessarily nearly as exciting, especially if the end is "a business". Business is necessary, sure, and I'd build things for business purposes as a job, but it's not my main interest.

That's probably even my reaction to the average startup on HN; for many, I don't really care about their SaaS or ecommerce solution or whatever, but they often solve interesting problems en route to getting it to work.