I’m not exactly sure when I started carrying an EDC (Everyday Carry) knife, but I’ve long held that it is tool without which no responsible Sheepdog leaves home (local laws permitting, of course). Most people outside of military, law enforcement and hunting/outdoor communities don’t understand why one would need to carry a utility knife in modern, urban life. EDC knives, however, are amazingly handy for basic everyday tasks like opening boxes or packages to various shrink-wrapped consumer goods (there are more than you think). Second, it is a last-ditch, emergency defensive tool that is legal is many places in the United States. While everyday tasks and self-defense are great reasons for carrying a pocket knife everyday, I think this video sums up the third and most important reason: you just never know when an EDC knife might save your life or that of a fellow citizen.
August 9, 2018 Update: I now carry the SOG Aegis folder for my EDC blade. I still use the Cold Steel CODE4 with dress clothes because it has a slimmer profile, but the SOG Aegis is just so darn light. The Blackhawk CQD Mk.1 Type E now rides shotgun in my go bag.