Between 2004 and 2012, I lived in New York City, made about $30,000 a year, and was able to sock away over $100,000 for use as a down payment for an apartment. I learned a lot in the process.
Surprisingly, though, my key takeaway doesn't have to do with either earning or investing.
Although it doesn't come up much in discussions of personal finance, I discovered that people matter most. If you make the right relationship choices, it's significantly easier to make the right money choices.