I honestly don't get how some people have totally forgotten "buy low, sell high!". It's common sense. I know people are always looking for some more intelligent, complex secret, but that's really it.
With Crypto it is so much more extreme because a bunch of new people get in whenever it is up (buying high, which you shouldn't) and then they all run when it goes down (selling low, which you shouldn't). It's pro-cyclical.