How do people react when they are fearful? What is the danger in acting out of fear?

When people react out of fear, they tend to react without
thinking.  They do not clearly think through the consequences of their actions. 
Instead, they just go with their gut reaction.  This can at times be very
bad.

From the way you've tagged this, I assume you are
talking about the Depression.  When people reacted out of fear in that era, it wrecked
our economy.  The people, for example, rushed to their banks and tried to draw out all
of their money.  This caused the banks to collapse and that made things worse than they
had to be.

So when we panic, we act without thinking and we
do things that can hurt us worse than more reasoned actions
would.