COLORADO SPRINGS, Colo. -

It's a question we ask after a celebrity commits suicide: Why would someone so successful and with everything to live for, take his or her own life?

Many in southern Colorado are wondering the same about actor/comedian Robin Williams. But an expert in suicide-related issues said Tuesday that Williams' suicide was more than just a celebrity unable to handle the pressure of success.

Janet Karnes of the Suicide Prevention Partnership said Williams and others who kill themselves share a common trait -- being in pain and seeing suicide as the only way to end it -- a trait possessed by average people as well as celebrities.

"We know that (Williams) had severe depression," Karnes said.  "That's a chemical imbalance in the brain, so it's not anything that anyone can control.  It's a disease.  Such depression can develop a narrow vision where you can only see what's wrong with your life, instead of what's good or of all the help out there."

Karnes said Williams' visit to a drug rehab center likely was another factor in his suicide.

"If he had a relapse, that's when people are most vulnerable to considering suicide," she said.

Karnes said she hopes the suicide of a celebrity like Williams will eliminate some of the stigma of suicide.

"Maybe if people see that if it can happen even to a celebrity as well-known as Williams, they'll see it can happen to anyone."

Still, Williams' death by his own hand was a shock to fans who had followed his career for nearly 40 years, since his appearance on the ABC show "Happy Days" and his rise to stardom in the ABC show "Mork & Mindy."

At Entertainmart near Citadel Mall in Colorado Springs, the staff quickly set up a rack of Robin Williams' movies.  A steady stream of fans arrived to buy or ask about his movies.

"I was sitting on my couch (when I heard of the suicide) and I just lost it," said Rose Moran, a Williams fan.  "I love him and he'll be missed."

Moran tried to understand why Williams no longer wanted to live.

"(Celebrities are) just regular people like you and me -- and they can't deal with stuff, either," she said.  "Just because you're rich and famous doesn't mean your brain is any different than a regular human being's."

Scout Andrews, 20, wasn't born yet when Williams became a household name.  Still, she said she's a big admirer of his.

"I would like to think that he just had so much knowledge and so much power inside, he really didn't know how to express it -- or he tried in so many ways to express it, in many of his movies," she said.  "I think that he was lonely and he was the only person who thought the way that he did -- and maybe that made it hard for him."

Ironically, in the 2009 movie "World's Greatest Dad," Williams' role was that of a father who wanted to prevent suicide.  His character, Lance Clayton, said:  "If you're that depressed, reach out to someone.  And remember, suicide is a permanent solution to temporary problems."