This isn't entirely true.
There aren't many coins that are being played or can be played as a "Long" investment.
Ripple is the finest example of a coin that just rode an incredible amount of hype to a price that I don't believe it ever sees again.
There's 38 BILLION units in circulation, with that number rising, so it is inflationary. It's not a decentralized currency, It went from trending around 25 cents... to $3.50 in a month (holy shit for anyone who caught that wave) but that was it... people thought it still had some legs, but absolutely not. There was no chance it was ever justifying that market cap.
And now it sits at a $1 and in my estimation, still terribly overvalued. If you bought at $2 or $3, you're fucked. If you bought at 25 cents... you should have sold, and outside of hoping for another pop this week back to $1.50 maybe, in the long run this is going back well under a dollar.
You have to be able to recognize unsustainable growth, irrational growth... and in those cases, if you happened to profit, get the hell out while you can.