In theory that’s true if you’re holding long term instruments with reasonably stable value and growth (which is not guaranteed for crypto currencies) and happen to have the liquid cash to buy. But in practice it’s often not true, as most investors who try to “time the market” end up underperforming the actual instruments they trade in.
It’s really not true if you have any leverage at all, where a crash might increase your margin requirements or wipe you out entirely.