Is a very harsh question. For instance, if you buy bitcoin from the inception, and sell at the price of 19K, the profit would be maximum as of current. Because nobody can tell if bitcoin will bounce back to 19K or surpass its glorious past. Right? But, not every coins holder bought at the initial price which means someone has lost a bunch of money. Bitcoin price is unstable and many signs of price fluctuation proved it is controlled in some ways. An educational article titled "Three types of cryptocurrency traders that are kicking your ass", telling people that need to be alert for the fake sign of bull market. My advice is, sell the coins at an ideal price which means you think the profit is considerable, and buy at the rock bottom of bearish market period next time. Keeping up with the latest news and keeping a sensitive smell of market. Don't be greedy nor timid.