I think refusals come from people not foreseeing returning to their set points (like they overestimate the benefits of winning the lottery). As of right now, I don't think Ebert needs willpower, or even thinks "Darn, this sucks" whenever he has to do something related to his disabilities.
From Mike Darwn's Chronopause, an essay titled "Would You Like Another Plate of This?", discussing people's attitudes to life:
Conclusion, graphs, and references in article. As usual, I recommend reading Chronopause.com as Darwin has many good articles; to quickly link a few: