Comment by mrweasel

But when it fails, everything fails at the same time.

It's not that far fetched that if your phone dies, you can't unlock your car, you can't pay for the bus, your insulin pump now lost its controller and you can't call anyone.

> A smartphone is a device you can pretty much guarantee people will keep with themselves

It's a device that many will keep, some might not, some will forget it, and seeing the state of some phones, you can't assume that it will be in good working order. Many apps will also require a relatively new phone, what if you can't afford a new phone?