I disagree: I built a "grocery list" app that I can access from my phone. If I'm buying groceries, and I update the list, someone else can view the up-to-date

I disagree: I built a "grocery list" app that I can access from my phone. If I'm buying groceries, and I update the list, someone else can view the up-to-date list and won't buy a second carton of milk.