It is also a very normal human emotion that needs to be expressed in a healthy way. (inc.com)
They spend their lives learning how to mimic normal human emotions, but they don't actually experience any of those feelings. (mindbodygreen.com)
On a side note, Patrick Gross does not respond to criticism well, and generally uses anger and violence to compensate for the fact he can not properly process normal human emotions. (waytooindie.com)