Most of the replies to this question that I've seen so far have been on the rather silly side but, perhaps, interpreting them as a unit provides a sensible response.

Looking back on my career so far, a period of nigh on thirty years, and I'd say that I am still trying to work out what I want to do when I grow up. That is a serious comment, despite its apparent flippancy.

To go into the comment in more detail: perhaps you are asking the right question in the wrong terms. Doing something new every so often is a Good Thing, in my opinion. I've a short attention span and feel the need to do something radically different every five to ten years.

What I do is keep interested in a whole bunch of different subjects; add new subjects every now and again; never stop educating myself in subjects that take my interest; join communities which share those interests; learn from those communities and contribute to them.

After all that, pay attention to opportunities that arise naturally and grab opportunities as they arise. Carpe diem, if you're classically educated.

In the interview for my penultimate job I explicitly told the interviewer about my short attention span. The reason was two-fold ---; to answer the question about my previous work history and to indicate that although I would work well for several years, I didn't expect life-long employment unless my employer could keep the job interesting. It seemed to work, in that I got the position. Indeed, I'm still there though working only 2 days a week now. The other 3 days a week are spent on the next opportunity to arise.

Paul