In my youth I used to fight Muay Thai professionally and did so for about ten years. I would be very confident taking on a random person in fisticuffs but I would rank my chances against someone with a knife very, very poorly.
Knives give an obvious reach advantage. Also just one nasty slice or one well placed stab and you’re fucked where generally most people will take a few well placed strikes to stop. The odds just aren’t in your favour.
Basically the safest thing to do against someone with a knife is run for your life or get your hands on a weapon that’s longer than the knife if you can’t run.