Ok, now I like your thinking here. The problem here is that 'facts' often refer to Te, where as you said he, "observed traits of his patients". That is Se. And it is common for ISTjs to be skeptical:

Quote Originally Posted by Pearl Eighty
ISTJ,ISFJ = To believe
Skeptical, critical, independent, determined, paranoid, sometimes stubborn… yep, that's me!

My family has joked that I BELIEVE NOTHING AND NOONE. Although I don't have to see and feel everything to believe it, I do require overwhelming proof and a healthy respect for your intelligence to be persuaded.
If you look at my previous posts, you will notice that I used words like 'observe' and 'persiverence'.