I do not think there is straight-line cause/effect between single groups of actions and disease. Yes, maybe not having a "purpose" can help one's propensity to develop a disease -- my father died and my stepmother quickly got senile/went downhill. However, I don't think anything is quite so simple that one can get a straight line bead on cause/effect in that way.

"People who are more motivated tend to recover better after a stroke" - but are they motivated to recover from the stroke or motivated to get back to their job or being race walking champion in their age class, or what? Does that matter? People who are younger tend to recover better after an illness too, those who are in better health or physical shape to begin with. Where do we put the emphasis? I think it is the nature/nurture argument all over again. If I am a committed writer and the left part of my brain is injured in a stroke, my being a committed writer won't help me much, I need other skills if I am to recover well?

I don't think motivation/commitment is a static thing where you have or discover "a"/"your" purpose and the rest of life goes swimmingly. Everyone has to die of something and the older I get, the more I realize that there is really less under my control than I thought there was when I was younger. I think one gets swept up in various "obsessions" like weight, food, jobs/working/occupation, exercise/the physical body, health, family, purpose/personal growth and expression and take whatever is of interest to an extreme that has to "unbalance" one somewhat. One cannot be all-in in one place and not be neglecting another which may/may not be important. Planting one's self in the sun but neglecting how much rainfall the area gets/is needed does not work for very long. Suggesting everyone drink 8 glasses of water a day when some are planted in clay soil that retains moisture, rots the roots?