^
Herd mentality somehow got a bad rap in this herd of special snowflakes.  Herd mentality is an adoptive behavior, herd animals fare much better within the herd than outside it.  Going against the herd may seem romantic, but it's not life-affirming.
/tangent
Anyhow, knowing about "herd mentality" nets you nothing.  If you see everyone selling (tanking the price), you should also sell (the price is going down, regardless of it being irrational).

TL;DR: Everyone panicking is cause enough to sell.  Due to panic or common sense, doesn't matter, the result's the same.