It's really regret for those who learned about Bitcoin in 2009 but didn't hold it. At that time many had enough money but didn't collect Bitcoin because they couldn't trust it. Today they feel that their golden period has passed. Now those people only regret. Time once gone never comes back. So we should give importance to the present and get better in the future.
Instead of losing hope about making that kind of profit again, and being hopeless and being sad at all times, just realize that bitcoin could still make you some profits and invest anyway? I mean just because you forgot to invest 13 years ago, or didn't invest 13 years ago, doesn't mean that you shouldn't invest right now neither.
If you invest right now and make 5x return instead of 50x return, that’s still good, it’s better than any stock that could profit you, or any other investment. That is why I am still in full support of bitcoin and everyone should be as well. Do not consider yourself as missed an opportunity, consider yourself as you have a chance in the future.