We regret about missing Bitcoin, then about XRP then about Ethereum then Doge then Shiba then Pepe (these are some top of my head and from what I've come across in my crypto term).
Point being there are always new opportunities and dwelling on regrets is futile.
Damn true 100% I'm currently going through a phase like what you're going through and it's even worse losing 95% of my portfolio, to the point of severe stress, maybe it's almost depression. But now I'm trying again to get up, even though it's very difficult, sometimes the feeling of trauma comes suddenly.
The biggest and noblest capital in life is experience, from that experience it becomes something that can sustain all life to bounce back and continue to learn from mistakes. Think of it as knowledge and life lessons so that it doesn't happen again. Of course, emotions have a big influence on making investment decisions. From that mistake, I had to learn to control my emotions to be better in the future.
You can regret it and feel disappointed about the loss, but really, believe me it's completely useless when you don't manage to learn a valuable lesson from the experience. The fact is that many people are more careful and tend to be better when they have tasted how bitter it is to lose when they have worked hard to build it, but that shouldn't make you just give up.
You know, these bitcoins and cryptocurrencies continue to grow and develop from year to year. You will succeed in getting the target you expect when you start to realize how and what you should do and what you shouldn't do. I've suggested avoiding altcoins as a long-term investment, but altcoins are also good as part of diversification. Just build your portfolio with as many bitcoins as possible, but feel free to diversify.