I believe in years to come people will be telling stories of how they had x amount of btc in 2015. They will then be asked why they aren't now rich as Bitcoin has now become widely used and therefore the price is very high.
This is when the idiot has to admit selling his btc due to making $chump change profit at xmas that year and not buying back in when they could.
We cannot be sure that bitcoins would be widely used after 10-20 years as now to people doubt its existence. Selling bitcoins is not a bad thing as money in hand is aways worth rather than holding it for years and then counting the losses. This I can say as people are still regretting buying bitcoins when the price was $1000 or more.
No one should actually regret, some think that Bitcoins are ponzi...
Just take a minute and think, if Bitcoins were ponzi, then it should have been completely destroyed when that dump took place from $1.2k to $120...
Some would have made more than x1000 with their old mined coins, while some would have lost, but only if they sold, else the opportunity is still there, but they need to wait, else if they got out, it's their decision...