True, in a knife fight you’re probably going to get cut. There was an infamous case in Tucson some years ago where a U.S. Navy SEAL was stabbed to death in a restaurant parking lot following some type of stupid encounter. Anyone is vulnerable, no matter their training.
If someone is just an average joe armed with a knife, you might have a decent chance with training. If the guy with a knife has knowledge of how to use one properly and you are unarmed, run-fu is your only real option unless you have a gun or some other projectile weapon like a taser.