I hate it when people say this as a response.

If I'm on a bridge, and people are jumping off en masse, then one of two things is happening:

1. They've all been mentally affected, in which case, I almost certainly am too, or;

2. They know something I don't.

It's disingenuous to throw out a contrived example of a herd of people nonsensically jumping off a bridge. If that many people are jumping off a bridge, you probably should too, because they probably know something you don't (yet).