Buying altcoins, I have always had one principle

Leading thought.

Don't use the theory of catching up. The leader can always be strong, and it can get stronger and stronger, with a clear vampiric effect. Only in the later stages do those catching up garbage coins appear.

Another method is to observe which altcoins are the most resilient during each pullback.

You can see this rebound; strong altcoins have already returned to their pre-waterfall high points, but weak ones have not returned at all. This is like choosing the wrong coin is like marrying the wrong man; even buying the dip follows the same logic.