The risk is in them disarming you and using it against you, which is likely to happen if they’re already the aggressor in the situation. If you insist on concealing it until just the right moment to surprise your attacker you better make it worth it and take their eye out. If you stab them in the arm their adrenaline will kick in and they’ll take it and cut you back. You ever see someone pouring blood? You got what it takes to keep stabbing someone when you see blood everywhere? Can you live with yourself after? I’m just echoing some of the things I’ve heard before when people talk about carrying a knife for defense. It’s not recommended.