Humor is like gratitude in that it nurtures optimism, and Dan Baker writes this in “What Happy People Know”:

"[Appreciation] is the first and most fundamental happiness tool. … Research now shows it is physiologically impossible to be in a state of appreciation and a state of fear at the same time. Thus, appreciation is the antidote to fear."

So if humor can change a perspective on a painful memory of the past or a gnawing issue of the present into opportunities to laugh at the inherent craziness of life at times, then a person can better facilitate his own healing.