In a class I took last year in social work, we were discussing medical/end of life issues and this one young lady was adamant that were she to ever be in a coma, she'd want to be kept alive by all means possible.
I understood from other things she said that she's a religious person who probably believes in miracles and I did not want to attack any of that but I asked her some simple questions: "How do you intend to pay for that? Have you already started budgeting for your coma? How much have you saves so far for being a vegetable later?"
She looked at me in shock. I don't think she'd ever considered that aspect before. I told her that I have no problems whatsoever with her living her life the way she wanted. But I described some of the costs of keeping her housed, of keeping her fed, of the tubes going in and out, of treating infections. I said, "where's all that money coming from to keep you alive on a table, me?"
But also, even if someone doesn't believe in miracles, often they believe in science. They hold out hope that if they can just stick around a little longer, that someone will find a cure. And so instead of using that window of opportunity to end their own lives with dignity and without suffering, they hold on until it is too late and wind up suffering through years of dementia or months of some delirium either from the pain of their infliction or the medications to reduce their pain.
There is a lot of discussion about how to live a good life and yet so many fail or have much trouble with that. There is almost no discussion (at least in Western culture) on how to die a good death. So what are the odds of success with that?