Suppose you had a disease that was in some way debilitating, so that it limited the things you could do in life. Now suppose that there are two treatments for this disease, one of which alleviates some, but not all of the debilitation, and only restores some of your original expected lifespan, and the other which would completely cure you, but also had a 1 in 3 chance of killing you (essentially Russian Roulette with 2 bullets).
Would you prefer a guaranteed 18 years of life at 2/3 of your "capacity of living", or would you take the 2/3 chance of living a 18 years at full capacity?
Are these equivalent in your mind, or not?
As a risk equation, the two appear to have equivalent value assuming that 2/3 capacity of living value is assigned by you, and not by anyone else.
However, what this equation fails to account for is adjustment to limitations over time, and increasing improvements in our healthcare system.
I don't think I'd ever take the high risk treatment option simply because I live in hope, a) that as I adjust to my limitations, I will still find ways to remain happy, even though that will take time, and b) that in the 18 years that I have at 2/3 capacity, the medical system may find things to improve that to 3/4, or 4/5 or even to a complete cure.
It is interesting in looking at medical decision making models that this "Hope factor" hasn't necessarily been considered in many of the models I'm looking at this term.