Which is why trading is so hard, sometimes the best thing to do is to grab profits as fast as you can but if the circumstances change a little bit then the best thing to do is to not sell your coins and keep holding them and wait until the price raises significantly
Trading is hard when you do not know how to deal things efficiently. The choice of booking profits or continuing with your stash should be decided by your technical analysis but not just due to situations. There are versatile tools and indicators are available which will show you when to book profits and when to keep going. Selling at peak and then buying back is good but for that you need accurate predictions which may not possible all traders as anyone can perform well by experience and making use of what they do learn continuously.
this is why trading cannot be learned by just watching a few videos in Youtube with people that are not that good at trading.
Trading is not about learning alone but experience. Learning is just 30% of preparation and the rest of 70% is on how depth your experience is. Learning from books/videos/other traders and then practicing in demo account is the way I do follow till now even I have been into trading for more than a decade.