I've seen some mathematical calculations here recently where you lose more if you don't sell when you fall. Look, it's quite an interesting article.
But that depends on how deep the chart of altcoin goes. I have seen that so many times when someone was trying to sold their shares on the bearish market with the hopes he can take another bottom but after that there was a rebound on its price and then that makes sense if that will be involved a very high risk.