What appears to be miserable may not be so. For example, there is a man who is paralyzed on one side by accident and lies down in a hospital. He may have become so on account of the karma of his previous lives or for his own study. We are born because we need some experience. He may have become so because he needs the experience of living this life with a disabled body.
Stephen Hawking is disabled, but, beyond the limits of his handicaps, he has found a better life than normal people. If you look for it, you will find many such cases. There have been many people who were born disabled, but bright and innocent. And they lived outstanding and wonderful lives. They may have been given such tasks to be an example. That is beyond human judgment.