It really depends how you define success.
A lot of my friends are healthcare professionals, teachers or work elsewhere in the public sector.
All work their arses off, contribute massively to society and their communities but none would probably meet the usual definition of success. Most don't own their own homes, don't have masses of cash and all that, they get by.
Other people I know have big houses, money, nice cars and holidays. The vast majority of those were born into privilege and have had a lot of help to get where they are. Funded through uni, deposit help from parents etc I don't doubt there's a fair bit in nepotism too.
Many work in finance, making other people rich in sometimes dubious ways.
I don't believe that hard work alone makes someone successful by any definition. Some people will work ridiculously hard, long hours in low paid jobs and will never be able to do much more than break even. It's very insulting to imply that they're just not trying hard enough. I see the spirit of Thatcher is alive and well!
So for me, to meet the popular definition of successful, I'd say it's about privilege, some luck, some hard work and often making ethical decisions about the sort of career you want to pursue.