If you have a normal brain, you take reality for granted. It stays relatively fixed, and your brain stays relatively transparent. You think with it but not about it. Life goes on.
But if you have a brain in which the chemicals wreak havoc, this is another story. Voices inside your head can be as real—or more real—than those of the people around you. Reality can change from day to day. One day the world is painted with the darkest colors of gloom, self-deprecation and utter joylessness. The next day you are invincible, capable of anything. You drag your body around as dead weight, and your thoughts race so fast you can’t keep up with them or make any sense of them. One moment you are virtually immobile, and the next you are on an irrational manic spree.
This is what the life of Robin Williams was, probably from early adulthood, if not before. And this is what the life of many mentally ill individuals is like. And there are many tragic endings in a culture where mental illness elicits shame, treatment is expensive and not always accessible and medications can be unreliable.
Robin Williams made a difficult choice, and no one will ever know the mental and emotional circumstances surrounding that choice. But the unbearable pain is gone pain which not even fame, wealth and public acclaim could erase.