When I was a teenager working at a Subway in Sumter, South Carolina, I used to get corrected for something that seemed small at the time. I would build a sandwich, stack it high, and make it look generous. My boss would walk by and say, “That’s too many tomato slices.” I didn’t understand it then. I thought I was doing a better job by giving the customer more. But he would calmly remind me, “Those extra slices add up.” At that age, I thought he was being overly tight. Years later, I realized he was teach ...