You can really see it in his face, especially now, with his emotions when you re-watch his movies. The best actors always have the relative experience to pull from in order to reach certain depths and the best comedians are always so depressed. What they say is funny, genuine, but their frustrations are relative to so many people who just don't have the courage to stand up and say it to the world. They're pulling from something real to them. Jim Carrey's quote come's to mind, "I wish everyone could get rich and famous and do everything they ever dreamed of so they can see it's not the answer". Surely Robin Williams started in comedy and acting because they were his passions, his release, and he never planned to become who he became along with earning what he earned. At this point in his life he had probably done everything he ever dreamed he would do but even before that was never truly happy. It's funny because I talk to some people about traveling the world on the means I had and they say, "wouldn't it have been better to fly in your own private jet, stay in luxurious hotels, have sex with supermodels, etc..." but they forget about the experience, the hardships, and the relationships bonded. It's like when you're younger having sex with every hot girl is your goal, it's great, but then you realize it was never as good as with the woman you actually love even if she's not the most attractive woman you've ever been with. I can see how even a millionaire would be depressed. They can have everything and yet nothing at all.
RIP Robin Williams