Wisdom: The Cockroach Theory

Every day, I meet with someone that teaches me something about life. That's the good part of working in an organization where you throw a stone and there's a 50% chance that you'll hit someone who has worked at least 15 years in this company. Today, I met with RR (he's retired now) and he shared with me his greatest investment lesson - the Cockroach theory: whenever you see 1 cockroach, there's bound to be more of them. So if there's a negative surprise, don't wait- just sell the stock straightaway before the massive downward price spiral. It's not always right, but it's right 19 out of 20 times, says RR. That's quite quite hard to do in practice. I wonder about its application to relationships - might that hold too?