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A Coin That Triples Can Give It All Back With a 67% Drop
Percentage moves aren't symmetric. NEAR's 198% month would be erased by a fall of about two-thirds, and Zcash showed in June that a coin can fall 61% in just over two days.
Gains and losses measured in percent don't cancel out. A price that rises 50% and then falls 50% ends up 25% lower than where it started, because the fall is taken from a bigger number. The larger the moves, the more lopsided this gets, and in a week when several coins have doubled or tripled, it's worth doing the arithmetic.
Take NEAR. It rose from $1.824 at the end of August to about $5.44 this weekend, a gain of roughly 198%. To return to $1.824 from here, it would only need to fall about 66.5%. Going the other way, a coin that has halved needs to double just to get back to even, and one that has fallen 75% needs to quadruple.
Falls of that size are not theoretical. On June 3 Zcash traded at $644.51 on Binance; by 07:00 UTC on June 5, amid a broad crypto sell-off, it had touched $250.12 — a 61% drop in about 55 hours, most of it in the last 30. From that low, ZEC needed a 158% rally just to get back to where it had been, and it did not trade above $644.51 again until August 21, eleven weeks later.
The practical point is about what a big percentage gain tells you. It measures how far the price has come, not how much cushion there is. For position sizing, the more useful figure is how far the asset could plausibly fall from here, in dollars you're prepared to lose.