That's the hardest part: watching a flashing intellect wither and die. But here's something even harder: I have a brother-in-law who's always had a brilliant intellect and who was a lot more than just a brother-in-law; he was a very close friend. He has Parkinsons (why would anyone want a disease named after him?). The flashing intellect still is there, inside a body that can't walk unassisted, and can't talk well enough to make use of that intellect. That's even worse than watching a much loved person sink into dementia. I know my mother was happy and comfortable in her distant state. She'd talk about visiting her dad, who'd died decades earlier, and smile as she told about her visit. But my brother-in-law is still here, in this daily world, but trapped -- as surely imprisoned as if he were in a barred cage.