Yeah, there is nothing wrong with taking a profit when the market is at its peak, this is something that varies for individuals, some people don't want to take a profit until the price reaches their target, and others do so when there is a reasonable rise in price.
From my little experience as an investor in this space for some time now, it is best to take profit, especially during the peak period of a bull run, once that period ends and the bear market comes in, you will be filled with regret for not making the move when you had the opportunity.
Here is the problem, no one knows the "peak" of the market, hence they hesitate to sell their coins. Don't you think if people knew what the peak was, everyone would be selling at the peak and buying during the dip? Everything would be easy with no risks involved. Again people also hesitate because of the past. I am sure there are people that thought $15,000 was the peak of bitcoin and sold their coins only to later realize that the price never went back down below $17,000.From my little experience as an investor in this space for some time now, it is best to take profit, especially during the peak period of a bull run, once that period ends and the bear market comes in, you will be filled with regret for not making the move when you had the opportunity.
I think a little differently, in my opinion, buying and selling of coins or tokens should be done looking at the whole situation of the crypto market and not the profit or loss. As at the moment if a project gives me a profit, I will not take that profit until the crypto market reaches a new all time high whether it is made in a month or a year.
In other words, you won't sell until you reach your profit goal. This is what most people do I think. Less risky, but slow. 
