I stopped for a few items at a popular grocery store in Manhattan on my way home and pulled out the nylon shopping bag that I sometimes — but not always — have tucked away in my purse. “Thanks for bringing your own bag,” the cashier said. “Guess how many paper bags we use a week?” she asked me. I really had no idea. “Five tons,” was the answer.

I haven’t been able to stop thinking about that number. Five tons of paper a week for one (granted, very busy) store just for grocery bags. It put the issue of making sustainable choices in terms that is hard for me to ignore — and illustrated how critical it is to keep working on the sometimes unglamorous, but very neccessary, work of changing behavior.