Absolutely true. Another guy mentioned to take out 10% each time it doubles which is also a good thing.

As for myself. The initial investment I like to take out in the midterm. In case crypto would be a complete failure (which I think is highly unlikely as of now) I wouldn't had lost any (fiat) money.
Differentiation is key, not only in crypto, also compared with other asset classes. In case one single coins sucks you will not take a heavy hit.

Before I make an investment in crypto I have a plan when to sell it. This can be "only" 20%, 100% etcetera. If it reaches it i will immediately realize it.

Another option I sometimes apply is: On some exchanges I adjust sell orders when the price keeps going up which gives me additional profit.