It depends on the investor itself, as an investor we should be seeking for a secure profit and not a high profit and if we're looking for a high profit then we should just invest into gambling. For me the art of quitting is easy you since my goal is just 3%-5% of what I've invested and moved to the next coin or to wait for the right investment again.

in regards with losing I'll set a 5%-10% of losing before quitting my investment in order to avoid further loses since we don't know when will that coin will pump again.