why did charlie seem so afraid that the doctor would think he spilled the ink on the inkblot

Charlie was worried about the ink blots because he thought they meant he's failed the text and would not be used in the experiment.

I had a test today. I think I faled it. and I think that maybe now they wont use me. What happind is a nice young man was in the room and he had some white cards with ink spillled all over them. He sed Charlie what do you see on this card. I was very skared even tho I had my rabits foot in my pockit , because when I was a kid I always faled tests in school and I spillled ink to.

Because when charlie was a little boy he used to always spill ink