In Monsters Inc. Boo fights back against Randall and gives Sulley a chance to grab him by the throat and restrain him. Boo roars at Randall as Sulley holds him and Sulley says something like:
She's not a afraid of you anymore. Looks like you're out of a job, pal.
Randall then gulps.
They had a case earlier of a child not being afraid of a monster and they just shredded that particular door. Each monster has a stack of children they work with so why would Randall be out of a job because one child is not afraid of him?