This points to the advantages of 1) awareness, to detect and avoid the impending attack before the attacker gets within range; 2) longer-range weapons, such as guns, canes, and perhaps even pepper spray (although this is unreliable) to damage the attacker before he gets close enough to cut you; 3) BALANCE for effective long-range kicking to try to again create damage before the blade can reach your vitals (steel-toe or otherwise hard shoes certainly help too!); 4) going to the ground in some circumstances to create more distance between the blade and your vitals while allowing you to dish out serious damage with both legs; 5) the Dog Dig tactic to keep the blade away from your vitals while you try to get distance and damage him; and 6) LOTS of good contact flow practice and hand training to enable you to SHUT HIM DOWN as quickly as possible at close quarters while staying away from his weapons.
Finally, remember that in a lot of real assaults, the victim is not even aware that a knife is in play until it's too late. That's why we always reiterate that you can't take any violence lightly, you never know whom (or what) you're dealing with, avoid violence at almost all costs, and if you must go hands-on, END things as quickly and decisively as possible. Wasting time trying to "control" the uncontrollable or second-guessing yourself can spell your doom.