As the word says "buy low and sell high" sounds too easy but the reality of it is that it is very hard to be executed for the fact that knowing when to buy and sell is a challenge already that even long time traders are still having a hard time to put into proper timing.
Yes mostly it is not possible to predict the price of coins but at certain points, you can. Recently Elon Musk made a tweet announcing that Tesla has suspended vehicle purchase through Bitcoins and one would easily guess that the price of bitcoins will come down by some margin and it did, so you can use those timings and trade.
For those who are impatient, of course they will have difficulty getting profits even though this method is the simplest and most common way for traders
Yeah, most traders are impatient for right opportunity. When you are in hurry to grab anything then you may grab losses as well. If you are too conscious on choosing right entry points then probabaly you will minimize number of losing trades which is the key for persisting longer in crypto trading.