The right time to sell is when you're totally satisfied with your profit; there's no specific years 'coz you could either sell after 10 years or 10 months depending on you as the investor. Some would say hold 'til $100k and there will be people telling you to sell already 'coz there's a tendency for a dump to occur given that the market has been 'up' for a couple of months. Bottomline is having no assurance of which way will its market value go; either up or down without any clue of when will such movement occur. So better focus establishing a 'winning' mindset; if you're down to hold for years or decades then you are free to do so and same thing goes for short term holders. No other people can dictate what's best other than the investor himself 'coz we are all just guessing the next price movement.Taking profit is indeed necessary and no one requires us to 'move' our assets fully and as a whole. It is a great idea taking partial profit given the fact and as mentioned above that no one can guarantee that its value will reach xxxxxxxx amount. At least, if ever something negative happen, you're still in profit with no loss at all.
Problem is with people who are comparing early investors to investors at the present without considering why some of them really managed to do so. Some of the early investors did not really anticipate its value right now. Some even forgot where their hard wallets are placed, and just happened to see it when the price is already 'up', which is fortunate of them. Some sold it already and basically, we are just having this impression of them 'coz we know to ourselves that we will do the same thing before only because we already saw its potential turn to reality. That's basically how regrets work.