The loss of Robin Williams is a harsh reminder to anyone who has lost a relative or friend to suicide. For so many people, such recollections are riddled with a feeling that had one more phone call been made, one more visit paid or extended, an ounce more empathy or sympathy expressed, the outcome could have been different. It's a heavy burden to carry, the pain perhaps second only to the loss incurred.
Rationally speaking, there is likely nothing anyone could have done. Williams had access to the best mental health care, unlike so many millions of sufferers. In the U.S.A., more people die of suicide each year than in road accidents.