> Is it more important to be right, or to be happy?

Im going out on a limb here, but I'd say intelligent people will tell you - without a doubt - being right. Because being happy is a perception and always a transitive state. There's nothing holding you from being both right and happy.

> Nobody likes to be told they're wrong

Thats actually a southern european way of looking at things; Its a cultural trace that varies a lot by region. Pointing flaws in plans is actually something I saw as worthy of an appraisal in Germany.

Also, I always tell people when I think they are wrong. I no longer insist or argue, just point out what lead me to the conclusion; you don't want to be in the blast radius of a deaf manager, an incompetent colleague or a delusional partner. Win-win.