imagine all those people who sold Apple, Microsoft, Amazon in the 1999 bubble. I bet they own those stocks again, probably cashed out and bought a lambo, only to buy back the shares at double to even 10x the price. will the same happen to bitcoin?
Likely, I will point you out to a good thread,
Wall Observer BTC/USD - Bitcoin price movement tracking & discussion, it's a lot of pages, but I'm sure you will read this kind of strategy specially for early bag holders. And it make sense though, nobody thought that bitcoin will gain so much growth that those early sellers wanted to get back into action and be a bag holder, sold some at an all time high, and then continue to accumulate during bearish market.