If you are looking to book your profit it is a wise decision to book them if you think that the market could go down. Assuming that the investment you make are extra funds you should book profit once in a while rather than holding for the infinite long term and for that you need to study the market trends carefully and sell everything once the trend reverses and wait for the market to settle down to enter once again at the bottom.
You may be correct only time will tell but I have no reason to believe that the market will ever come down again and I would instead suggest that the price of bitcoin is only going to go in one direction and that is higher. My reasoning for the advice is that now big companies are embracing and accepting bitcoins like Tesla Motors did some time ago. Would you sell something that the market is otherwise trying to buy? I wouldn't.
2017 is very similar to 2021 and there is a hope that BTC will be able to reach $ 100,000 for one coin, but everything can also change dramatically and go not according to plan.
In 2017 the price went massive because it might have been planned and organized by some big investors as they usually do with small altcoins, pump and dump, they might have done that with Bitcoin and later dumped the market. This year like I said above, big companies and investors are embracing bitcoin and I think the raise in price this time is genuine and not planned.