Most startups try to build another database, web framework, or data service, or whatnot, because that's the problem programmers are familiar with. The next ones are consumer products, assuming consumers look like SFO. The competition is fierce, and very few succeed.
My experience is that in virtually any other industry -- I don't care if you're in construction, shipbuilding, or farming -- there will be many low-hanging fruit which people in that industry won't be competent to solve. If you:
- go into some (nearly random) industry;
- keep your head up enough to gain an understanding how it works; and
- build out a network of connections you trust and who trust you
entrepreneurship is easy.
I guess the other piece is keeping your toe deep enough in tech that you can pull together a good team and solve problems a typical IT department can't solve. But that should be the easy part for readers here.
You can even start consulting. In the same way as a tech company doesn't want to outsource its core competency but is happy to outsource legal, payroll, and similar, the opposite is true in most industry. I've seen industries on HN where you (the typical HN reader) could outperform a whole 20-person team because the tech they hire is so incompetent. That's not a tough sell.