It's hard to predict which out of thousands of alts will go up, but what you can predict is that once a coin went up, it's bound to go down. Like, take the best performing coin right now, Dogecoin, there's absolutely no justification for its price, it has no adoption or promising features, it's pure hype. It's bound to go down, so if you carefully short it with small leverage, you're going to make profit. Obviously, the danger is in the known trading wisdom - "the market can stay irrational longer than you can remain solvent", but still the fact that pumped coins will go down is something that you can rely on.
And it will go down fast when the hype is over and the whales are ready to take profit, doge is a perfect example of a hyped coin with no strong utility or usage but still pump like crazy anyways.
the reason why some people not shorting it is greed (for those who bought in early) and those who is buying now really need to be on the look out, dogecoin already too pumped for any sane investor to be buying at this price, not a good decision in my opinion.