There is an old saying in the investment circle: if you want to make real money, starting at 40 is the most stable — provided you haven't lost your principal before turning 40.

This may sound a bit harsh, but there is scientific support. The human prefrontal cortex generally fully matures around the age of 40, and that part of the brain is responsible for rational judgment and risk control. In other words, when we're younger, our decisions are often mixed with too much passion and intuition, leading to overestimating returns and underestimating risks.

But this creates a painful paradox: the market's super cycles often don't wait for anyone. Whenever a major bull market appears, I realize I am still in the "learning how to trade" stage. By the time I have gained experience and become more rational, the next big wave is almost over. So, many people's regret isn't losing money, but missing out on those gains they could have enjoyed, simply because they were too young or lacked emotional stability, and ultimately missed the opportunity.