In 1983, when I graduated from the University of California law school in San Francisco in the United States, our commencement speaker was Robin Williams. He had been chosen by the students to deliver the speech.

His speech that day was brilliant. He was irreverent and respectful, as well as funny and serious. When I went to get my diploma, I ignored protocol and walked over to shake Williams' hand. Subsequently, other students did the same thing, and I don't know why - whether it was that break with tradition or Williams' words - but that was the last time the law school allowed students to pick their own speaker.

Too bad. Williams was the consummate pro. He had spent two days on our downtown campus walking around with students, attending classes and had done the necessary research not only into law but our faculty as well. He knew his stuff.

The first e-mail I got about Williams' apparent suicide came from a friend who was charged with recording Williams' speech that day more than 30 years ago. The two of us have listened to the recording of Williams' speech many times over, celebrating his words.

After I learned about Williams' death, I spent Tuesday searching online for his comic routines and found myself once again laughing hysterically for hours while sitting in a Ho Chi Minh City hotel room.

Quite simply, along with Eddie Murphy, Williams was the funniest man I ever heard. He epitomized for me, and many of my contemporaries, the absolute zenith of humor. And this is what makes it so hard to understand his suicide. Here was a man who brought absolute pleasure to millions of people, a man who could send people into paroxysms of pure joy but apparently could not outrun his own demons.

Ironically, my article on suicide was published in China Daily the day Williams' death was made public. And although I've written on suicide for China Daily before, I don't claim to fully understand the phenomenon.

Given the widespread reports about celebrities suffering from depression, people may tend to believe they are more likely to get depressed and even commit suicide. But as frequently happens when one examines evidence scientifically, it's not really clear whether celebrities are at greater risk of going into depression and committing suicide than ordinary people.

The reason why it seems celebrities are more vulnerable to depression is a phenomenon called the availability heuristic. It means that we use mental shortcuts to assess the frequency of events by how readily we can recall them, how easily available the information is to our memory. Because we are constantly bombarded with celebrity news, including the stints they spend in rehab centers, we assume that more celebrities suffer from depression and commit or attempt suicide than the rest of us.

What we can conclude from Williams' suicide is that a sharp increase in suicide rates, often in connection with severe depression, is part of a trend among Americans of his generation. According to a 2013 report by the Centers for Disease Control and Prevention, there has been a substantial increase in the suicide rate among middle-aged adults in the US.

The 63-year-old Williams fits into a troublesome suicide demographic. The age-adjusted suicide rate among adults between 35 and 64 years in the US increased from 1999 to 2010 significantly in terms of statistics, according to the CDC.

A study published in the September 2014 issue of Social Science and Medicine found a strong positive correlation between unemployment rates and total suicide rates over time in US states. Other studies show that some of the buffers which may have mitigated suicide among Williams' baby-boom generation - religious affiliations and close family ties - have broken down, thereby contributing to the increase in the suicide rate.

However, we should reject simplistic explanations about celebrity depression and suicide. There is no larger message to be gleaned from Williams' death than that he was a troubled man who nevertheless contributed a great deal to many lives.

The author is a psychology columnist.