I was eagerly sitting in my Experimental Psychology class listening to my Professor teach, as usual. Then, someone said there was a huge bug on the window, inside of the room.
The description (namely, the size) was enough for me; I didn't even have to see the bug. I got the heeby-jeebies, wiggled in my seat, and had the burning desire to continuously keep looking over my shoulder and side-to-side to attempt to locate the invader.
I heard the words the Professor was saying as he continued to teach, but could not process them or think about them for at least a few minutes. My mind was preoccupied, whether I liked it or not, due to the big bug. Despite my very strong drive to succeed in this class and impress the teacher, I could not pay any attention to him because of the very scary thing supposedly clinging to the wall.
I hope you see what I'm getting at, here. Next time your dog is afraid of something and "blows you off" when you ask for a behavior, think of my experience in my favorite Psychology class with my least favorite creature in the world.