For what changed my outlook on life? Xenocide - Orson Scott Card. The 3rd book in the Ender's Game saga, it spend a lot of time exploring how people with fundamentally different perceptions and interpretations of the world around them led them to conduct themselves in ways that conflicted with each other, but were virtuous and the right thing to do according to them.

Was a big help in helping me understand how empathy can help to resolve issues and how fundamentally different we all can think - be it medieval humans or alien beings.

https://en.wikipedia.org/wiki/Xenocide