For me, it's been about 3 things - expectations, risk, and excitement
Expectations: when I left school I decided not to go to university but worked and studied part-time - my reasoning was that I was hoping to get married one day and have children, so what was the point in getting a degree just to stop working and stay at home (rather now at how I thought). So I got a jib that was well within my capabilities and did some part-time qualifications too. That was all OK. I quite liked what I did, had a relatively secure job, and went back part-time after my dc1 was born. I could have stayed in that job and would now have been earning about £15K pa. Well actually, I wouldn't because the place I worked closed last year and my friends who still worked there are all redundant with very little prospect of finding something else.
Excitement: What I did find out (about myself) was that I liked learning and that I had more ability in some arenas than I had ever thought. So I did some more qualifications (part-time, with a young child, while working). Then I moved to a completely different career path.
Risk: I moved from a secure job to work on a 6 month contract. Because I believed there would be more opportunities, because I had some level of self-belief, and because although I liked my previous job, the new job intrigued me and excited me more.
Expectation: When I made the move I'd seen a job advert for a job earning £20K and I thought 'that's the job I'd like to aim for in 20 years time'. Within 2 years of moving job (all on relatively insecure employment contracts) I was in a post earning £20K. I learned such a lot about my own low-level of expectations from that. Not that they were bad, but just that they were unambitious.
Risk: I never stuck on a mainstream career track - I took opportunities that others thought were taking me off track, secondments to other organisations, transfers to different industries, posts in remote locations that required me to travel 2 hours to work and then 2 hours back again.
Excitement: And I always tried to do jobs that I loved.
Risk: Ten years ago, despite being in a well paid job, in a lovely organisation, my work/life balance was out of kilter, so I left and started working freelance - much to the horror of some people around me. My mantra was 'to do work that I loved, working with/for people that I liked'. And so it has been.
Excitement: The work I do now is nothing like the work I did 10 years ago (although it uses some of the same skills). I keep gravitating towards new challenges and new interests which keep me motivated.
Risk / Expectation: well who knows? I would find it difficult to guess or imagine what I might be doing in another 10 years time. But I believe I'll be happy, motivated, as successful as I need to be and satisfied with my income.
And apologies if all of the above sounds trumpet-blowing and self-congratulatory. I'm not super-woman, I'm not some kind of hero. I'm not even especially talented or gifted. I am good at what I do (although there are probably others who are better); I can manage to market myself (although there are others who would make a better job of it); I am motivated to do the work I do (although I can spend hours sitting on my lazy back-side staring out of the window).
I met recently with some others in the same 'industry' and a couple of them were commenting on my current work - along the lines of 'well it's alright for you, you've got experience in x' or 'well of course if I lived where you do, I could make that income' or 'well I can't make that commitment because my husband / child / horse needs to be looked after'. Yet from my perspective they have equal (if not more) talents than I have, and equal (if not more opportunities), and I have equal (although different) life constraints.
Sorry. This is probably not helpful to anyone on here, but I've enjoyed musing on it