It's life brother rather than regretting if they could have planned things for the future after realizing their mistake it could have been already covering their losses and regret brings disappointment so take everything in a positive way that what happened has already happened now plan for the future and take action in where you are now. If you will continue to blame your decision even now when it will go to the $1M which is for sure according to my optimistic approach for the next 10 years you will get nothing so its never too late just put in some effort and kick your ass for work it's fine.

No one knew at that point its gonna be that big, I'm sure 99% of pre-era investors did sold most of their holdings years ago but if they are still in I  market this shows that they are hustlers and maybe they are still millionaires.