Well, since this is a knife forum populated by enthusiasts, you probably won't find many here who only have one knife they carry. However, it's a perfectly valid approach, especially if you view a knife as a tool to get a job done and don't have any particular fascination with them beyond that.
I could get by just fine for all of my daily EDC cutting needs with a medium 3-blade stockman slipjoint pattern or a medium sized Swiss Army knife, while using task specific tools (utility knives, kitchen knives, scissors) for situations when the pocket knife is not enough.
I actually carry three knives with me daily - two on my person and one in a bag, that serve different purposes. There's some overlap and I could probably make do with just one of them, but having different tools suited for different tasks makes sense to me, and they don't add any significant burden so why not have more than one available.
Two of them are the same every day, the third slot is my "for fun" carry that I rotate though different knives just because I like the variety and enjoy using different styles and patterns.
But your grandfather was probably a wiser man than I and certainly less broke!
