Ideally, you’d know when to turn, even when you don’t. When you do, you shift your balance slightly, which in turn makes your left foot take a shorter step than the right one, successfully changing the general direction.

If navigating a grid of streets can be reduced to a mere balancing act, does it matter if that shift of balance comes from your brain — or from your bagpack?

After a just a few weeks of use, the thinking and knowing and anticipating of the balance bag and its novelty and excitement will start to fade out and disappear. The bag will change from a sensor to a sense. Your phone, the GPS chip inside it, and the GPS satellites 12,550 above you make sure that you know when to turn, even when you don’t.