Can prolonged exposure to someone else's negativity fundamentally change a person's outlook on life?

How can trying to provide respectable enough messages in their end up backfiring and exposing their own weak spots?
Why do some people prioritize their pride over friendships, and can this behavior be changed?
What was your rudest behaviour with somebody, and why did you do that? Do you regret it or not?
How can one differentiate between personality traits that are simply annoying and those that might be harmful or indicative of a disorder?