A knife is one of those items that is simple enough, light enough, and practical enough to carry it with you all the time (remind me again why you can’t take a knife on an airplane).
Knives have been carried for several hundreds of years and they haven’t been anything like what we have today. There are so many kinds of knives that it’s hard just carrying one. I need a pocketknife, a multitool, and why not a fixed blade; I’ll strap that one on my belt. Or why not a belt knife?
So many knives.