By karmic quirk every person who has asked why I carry knife has asked to borrow it at some point. Dishcore's list is fine but a better way to look at it is we're kind of squishy, our skin tears easy, and our nails bend. Whenever you need to go at something less squishy than you you need a pointy stick of something tough. I've pried things with the spine of a knife and I've banged on things with the butt of a closed knife.
The other aspect worth mentioning is convenience. When the tool-less ape runs into something he can't rip open with his fingers he runs off to find some scissors (cringe) or a knife. I have it right there. Like a keychain flashlight, it keeps you focused on the task at hand instead of running off to find really basic tools.
In theory you could get buy with one of these keychain multitools that are basically a small prybar. Knives are cooler.
The other aspect worth mentioning is convenience. When the tool-less ape runs into something he can't rip open with his fingers he runs off to find some scissors (cringe) or a knife. I have it right there. Like a keychain flashlight, it keeps you focused on the task at hand instead of running off to find really basic tools.
In theory you could get buy with one of these keychain multitools that are basically a small prybar. Knives are cooler.