Truth is: You would have sold long before BTC reached even its 2017 ATH of 20k USD.Seeing things in hindsight makes you feel dumb, but the real truth is that back then nobody saw it coming. Only few, very few people really believed in BTC as a store of value or whatever. If you could go back in time and told people in 2010 that in 2021 hedge funds, S&P500 companies and even insurance companies are buying billions worth of BTC at 40k+ USD and using it as a store of value, everybody would just see you as the tin-foil hat person, laugh at you and call you mad and delusional.
This is the reason why I generally feel bad for those "two pizzas are now worth X millions" posts, as if the people who traded BTC for goods in the old days could predict the future. As such, the moment your holdings were at 10x your initial investment, very, very likely you would have sold as well, or just bought that awesome thing you could suddenly acquire with magic internet money.
That being said, do not punish yourself with the "if I had" thinking. Invest what you can and hold while you can. Taking profits is not a bad idea as well.
I agree with this I used to think the same way too if only I had known Bitcoin earlier but the fact that I keep on using my Bitcoin or even converting it taking profit wouldn't change the fact the I would still be how I am right now and nothing would change even if I knew it earlier.
I also want to count myself as lucky to had known Bitcoin but for those new in crypto and holding their coin I assure you if you also had gotten earlier you would still be the same nothing would change if you couldn't hold it.
You might think that you are doing well right now because you are holding it because it is so easy to believe right now that the price would keep on pumping but once the market slows down or even goes down you might sell those coins that you hold to secure your profit.