Assume it's 8 years holding and never sell it until now, I find it's hard to believe because people are greedy and will sold after x3 or even x10.

But it's a interesting simulation to think how good Bitcoin is, there's no need to panic if Bitcoin goes crash... it's the opportunity to buy the dip.

Buy BTCitcoin.

Quite a fun simulation and all the very reason to have awe for the hodlers and envy for those who made it their side-hacks to earn Bitcoin through those years and are on different levels of financial self-realization as a result. I'd probably not have sold everything as I read Satoshi's and Hal's posts from early on.. Those are sufficient to convince anyone that Bitcoin was going to be valuable.

Its right that lot of corporates are now onboard and institutional interest is only growing. The real question is what would you do if there was indeed another flash crash. All these "institutions" are in it for hedging and as an investment. They don't give a damn about the technology as far as I can tell. Bitcoin's appeal is to the individual; for institutions it is another asset class. They can still cause sell-offs, hopefully. LOL..

Truth be told, most people definitely would've sold. But literally everyone? Nooot really. There are also a good number of truly avid Bitcoiners that has true conviction and truly believe in the movement that doesn't really sell unnecessarily. Including, me! I'll admit, I also sold a decent chunk throughout the days, but I wouldn't have sold them if I didn't really need to.

Had it at under $200 and sold it all. Next, bought it at $700-1000 and held it 'till this day.

As a quite early Bitcoiner, I can say it takes 2-3 such mistakes to finally learn your lesson. But I don't regret it. Would rather miss $200 and lower than not do so and miss $100k, honestly. You pretty much sell based on the influencing factors around you. For me, the reason to sell at sub-$200 was FUD.

or maybe even earlier than that. when it hit at 1k, for sure, you are already thinking a lot of profits at that time. imagine, from 100  to 1k was already a big leap. so you really cant tell in what stage you will sell. depends also in your financial situation. if you badly need the money, you dont care how much is the rate of btc at that time.
and youre very right, no such investment platform will give you such huge roi. and if few of those holders waited up until now, it is like you are already set with your retirement.

Retrospectively, no one would have had any idea of how high Bitcoin could have gone, so it's impossible to decide which price to sell at, even a 2× or 5× would have seemed like a very attractive offer which would have lured a good number of people out of their holdings.
How much someone knows about Bitcoin would have also been a factor, a person who is fully bought into the idea of decentralized money would find it easier to hold than someone who only viewed it as an investment option.

To answer the question personally, if I had bought at a $100, and it was my first purchase, I would likely have sold at a 2-5× range, ending up buying at a higher price when it shows more potential for growth. This cycle would have continued until I eventually understood more about the technology and how to draw up an investment plan.

Okay lets say that I'm one of the few who trusted Bitcoin right from the start and bought it at a very low price.
For sure that I will sell it when I saw my initial capital at x5 or possible x10. Why?? Because I didn't expect for Bitcoin to go even higher. One thing more is that I already set my target selling price.

That is how others are thinking. Nobody expected it to go at the current price we are seeing right now. When I started crypto back in 2017, the price of Bitcoin is at around 3-4k IIRC but didn't bought at that price. Again in March 2020, I saw it again at that price range but didn't bought.

Lets forget the past right now, what is important is the present and the future . Just buy Bitcoin and hold. Its the advantage of those early adopters to gain as much profit as they want to.

You wouldn't sell it because you know that the value of bitcoin will go up but if you didn't know and see a big pump like 1k USD a pop of bitcoin, I think that anyone is going to sell it. Don't kid yourself that you wouldn't sell it. Remember that the 50k USD is far apart from the time of 100 USD per bitcoin and along the way, there were past ATH and along that way, you are going to sell it because it was bigger than you initial capital.

One thing about historical data or charts is that they make us get filled with regrets and this isn't a good thing. BTW OP, it would've been highly impracticable (very impossible) for anyone who bought Bitcoin at $100 to still be hodling EVERY single Bitcoin they bought till now. Most of those who bought at that rate would've sold long before it crossed $10,000. The wise among them would split and sell part while allowing it run. The wiser among the wise would be trading to increase their quantity. Anyone who didn't sell any bit till now, either lost their password/PK to the wallet or dead (may be like Satoshi too). It's the same way a lot of us are hodling some penny alts now and we don't know what they will become a decade down the line. So, if we have any X5 or X10 profit, we quickly sell thinking that would be a point of dump. Who ever thought BNB would be worth this much today from the less than $0.30 it was listed in 2017? I sold my quantity when it crossed $3 with huge profit. But look at where it's today. We can't know the way these things pan out.