Why money comes prior to any, mainly in certain relations? I know it's the reason for our survival. But still, why pinch or fight over small things even casually? And later take it to heart affecting relationships.

People do know their responsibilities and will act accordingly. They might be just waiting for an opportunity. They might even plan to do something big making it a hidden surprise. Who knows... Trust is important. If it breaks, then every situation will lead to turmoil, blaming one side or the other. So, do act wise.