In any case, it is better to under-earn a profit than to close a trade with a loss. Therefore, you should not try to sell the coin on high, because in practice, only a few manage to do this. Similarly, you will not be able to buy coins at the lowest price. And this should not upset you.
Sell "high" in the sense that you should be profiting is the correct way to do it, sell "high" in the sense that you should find the peak point is the wrong one. I just wanted to clarify that because there are tons of newbies that may mistake the two. I personally do not sell at the high for both times, I sell when I feel like I have enough profit and I want to get out, I am a big time long-termer so I am always in favor of holding as long as possible.
But for someone who wants to learn trading, that means buying and selling quickly instead of investing long term. That is why it is always a big deal to get out quickly. I even used a bot to trade that calculated like all the costs and gave you 1000 satoshi profit each trade, normally you would profit even more because of the fee, but in the end whatever you traded 1000 satoshi was your profit after all expenses, the idea was to make tens of even hundreds of these trades, it worked like a charm until bear market came in.