After a while of living, most people experience diminishing returns and get jaded.

What do you suggest should happen to the people who don't get jaded?

Also, what if it turns out that it's only pain, sickness and death that makes people unsatisfied. There is, after all, quite a body of research that suggests people get more satisfied the older they get:

https://en.wikipedia.org/wiki/Life_satisfaction#Life_satisfa...

http://health.usnews.com/health-news/articles/2012/08/30/get...

http://www.pewsocialtrends.org/2009/06/29/growing-old-in-ame...