Life is about choices and we all are on the path led by our choices. It's not easy to talk about life regrets in general because we are/were in quite different situations. To make this thread easier, we just focus on the regrets in finances. I believe many of them can be lessons to learn from. I'll start first. Over a decade ago, I was living in a mega city of my country. At the time, the city was already a metropolitan place where you can meet all people over the world. Of course, the land was scarce and the price of housing was pretty high, nomal people could not afford to buy an apartment, let alone a house. However, one friend of mine was taking to a suburban area for an apartment, super nice but the neighborhood was not fully developed yet. The total cost of that departemtn was about $100,000. Well, I did not have that much money at that time but if I borrowed some from my parents and it was not a problem. Maybe because I was too young and did not get along with my parents at the time, I did not ask for that so I refused the offer and let go of that apartment. A few years later, the suburban area became part of the CBD and the housing price was going up insanely. Today, that apartment I missed is worth at least $1.2 million. Oh my... I hate myself for not buying that apartment every time I think about it.
I don't think it was your fault that you missed out on this opportunity. You didn't have the money to invest in the business and borrowing to invest is risky. If you borrowed and the place didn't appreciate this high, you would have been indebted which is burdensome.
I started a telecommunication business a long time ago and I later abandoned the business because I secured admission to a college. The business collapsed because of my absence. But the ideal thing I would have done was to employ someone who would handle the business when I do the supervision. After a few years, a major telecommunication company partnered with people that were in the same line of business as me, and many of them are millionaires now because the partnership opened more opportunities for them. Although I graduated with good grades, it would have been better to have a good certificate and a flourishing business.