I once got into a friendly discussion with a mudansha about knife attacks. He opined that a real knife-fighter would simply carve up any aikidoist stupid enough to try an aikido technique, as the strikes in knife fighting are very different than what we practice.
So, to test his theory, we tried it. I'd try and come in with a technique, and he would tap the tanto against my arm, leg, whatever, then dance away. After a few rounds of this I realized that I was (figuratively) bleeding to death, trying to take that knife away. And so, I came in with a full, open stance (not trying to take his blade away, this time), which threw the uke so off that I slipped in and gave a very satisfying koshi.
Whereupon I would likely have fallen over from loss of blood, were it a real fight.
But the point was made.