...part of what I will describe today will explain why it is difficult for people who feel optimistic and happy in life to understand people who are pessimistic and sad.
This is a fascinating post: a concrete framework for understanding why we are pessimistic or optimistic, with a discrete breakdown of factors, and a path to become a "learned optimist." I highly recommend this small post, along with – what appears to be – a healthy amount of follow-up books and posts. Being able to understand why someone has the outlook they do is important at a fundamental level for empathy, but also seems to be a prerequisite for change.
I'm currently working through "Thinking, Fast and Slow", and there is an entire chapter dedicated to optimism. Here's a brief excerpt:
Optimistic people play a disproportionate role in shaping our lives. Their decisions make a difference; they are inventors, entrepreneurs, political and military leaders -- not average people. They got to where they are by seeking challenges and taking risks. They are talented and they have been lucky, almost certainly luckier than they acknowledge.
This book has already had a profound impact on the way I think about the world, and I'd recommend it to anyone. But if nothing else, it's worth reading the chapter on optimism to understand the profound impact a mindset can have on your happiness, health, and success.