If you’re old enough to have grandparents who lived through the Great Depression, you might have memories of them holding onto seemingly idiosyncratic behaviors that were caused by enduring that traumatic period. I had a friend whose grandparents refused to allow condensed milk in their house for any reason. They experienced such severe poverty when they were children that condensed milk thinned with water was the closest thing they could afford to fresh milk. The scars from that childhood memory were so significant that even 50 or 60 years later, it still shaped how they lived their life.