i agree, but there are also ways to judge real life reactions.
one of my instructors will attack without warning, and attack hard, and generally while you are off the mat. he uses fake knives that look real, so on quick glance you can't tell (besides, they hurt like hell). the only way to see how you react under pressure is to add the element of surprise to practice. it's not 100% accurate, but it's better than forms or katas.