As a long-term holder, I just HODL. That saves me a lot of headaches and a lot of trading commissions. You just put an example of what newbies do: to buy after the last ath out of FOMO and to sell after the dip out of panic. This is the opposite of what I usually recommend
My style exactly. I don't want to be associated with all that daily drama of day trading.
In hindsight, I can say that holding coins and not dealing with all that minor price fluctuation is far better if you have a normal job and don't have time to react accordingly to ever-changing trading patterns.
I recommend only to sell, buy at major breaking points - ATH is a great time to sell and crashes and corrections are great entry points.
It has worked for you only because the market had been rising for well over two years, starting in September, 2015. If it starts trading sideways as many established markets do most of the time in some narrow or not so narrow range, you will see that this strategy is not as good as it seems to be. Further on, you don't know in advance whether it is an ATH or price is going to rise higher. But booking profits now and then is not what HODL means. Actually, it is half-way to day trading. The same applies to buying at dips. In short, a long-lasting sideways market will kill HODL.