A knife is really an experts tool. You need to be a skilled fighter to inflict a instant incapaciting wound. Stab someone in the gut or cut their arm and they may bleed out, eventually, but they will have a lot of fight in them. It is better than nothing but no way I'm going to tie up my left hand with one. If I carry something in my weak hand it will be a flashlight or spare mag.
"Suppose you were an idiot, and suppose you were a member of Congress, but I repeat myself." Mark Twain