They had faith and so would do things that were plainly not in their own immediate (or, often, long-term) best interests, because they just believed … - Iain Banks

Even though we thought ourselves by now inured to the thoroughly reckless nature of our opponents, we have been profoundly shocked and disappointed to discover the completely irresponsible and utterly senseless depths—or should I say heights?"—the ambassadorial emissary showed his teeth and glanced around his appropriately appreciative team—"to which our previously at least ostensibly esteemed adversaries have been prepared to stoop to in their understandably increasingly desperate attempts to secure a victory in this outrageously prosecuted, thoroughly unfortunate and—on our part—wholly unprovoked dispute.

“Let’s waste a little time, hmm?”
“A nice euphemism, sir,” she mused distantly. He smiled. “Come and help me think of better ones.” She smiled and they both looked at each other. There was a long pause.

Once one survives the trough that comes with the understanding that people are going to go on being stupid and cruel to each other no matter what, probably for ever – if one survives; many people choose suicide at this point instead – then one starts to take the attitude, Oh well, never mind.