Founding a startup. Two years before that I had very low self-esteem, due to having dropped out of a PhD program and coming back to my country, basically giving up the life I had built abroad over a few years. It took me one year to go back to being a functional person, and after one more year working at a company I felt confident and wholesome again.
Then I quit that company and co-founded a startup, to which I dedicated myself 100%. In 6 months we had a functional product. In retrospect, that might easily have gone south, but I had the good luck of choosing to build a product that obviously had a market, and the extremely good fortune of having great partners.
I never would have thought that one day I would achieve such professional and financial success.
I am an introvert and have difficulty making and maintaining contacts. Yet all of this was possible because of people I knew. On the other hand, it was my history of dedication, passion for engineering, and 'tackling difficult engineering problems' that led to people having a high respect for me and my abilities.
Introverts, consider that possibility that people respect and like you more than you think.