Regrets won't matter much because in the end we still have to move on. What I mean is that although we are allowed to regret something, in the end we have to move on because if we only lament what has happened then we will only be trapped with memories of the past that never end, which also does not make us grow.
That is true, but it's human nature to most of time feel that regret before we can moved on. it's going to be a life long lessons for this early investors and then sell and didn't have the patience. Maybe because they just jump on the bandwagon that year and so they think that it's enough for them to make that kind of money.
And to be honest, no one really knows what will the future holds, not even Satoshi himself. One thing that Satoshi might have known is that Bitcoin might be the future so he sticks to that vision but never seen it coming that it will be used as what we are currently doing, speculative assets, store of value, hedge against economic crisis or even "sound money".