With all the resources and connections necessary to make a big splash in any field? Well, then, I'd aim for something completely unprofitable.

But, of course, philanthropy can be ruled out. You'll want something with a high ROI, obviously -- but also exciting enough to justify 20 years of work.

Compared to 20 years of a person's life, the marginal dollar difference between Profit A and Profit B recedes to insignificance. Plenty of sectors can deliver a high ROI. Yet anybody with a soul -- yourself included -- will choose a field based on how much long-term interest it holds. And that's a personal, even idiosyncratic choice. No "expert" can advise you.

So I'm guessing you're essentially asking what sectors interest other people -- sectors, that is, with realistic space for profitable growth.

For me personally those areas would include publishing ventures and innovations for the digital property market.

But if I were a realtor, then I'd say real estate, wouldn't I? And if I were an app designer, then I'd say to you: "Apps, apps, apps, apps, apps". And so forth.

Apologies for the essay!