Having spent a considerable part of my life training ATCOs I do believe that some people are born with the peculiar ability to be air traffic controllers. One controller I recall was quite capable of carrying out the Heathrow Approach Radar task within days of starting (you reading this PW???) whilst others never made it despite months and months of trying. Others worked hard for ages and just about achieved the required standard.. and later became very good radar controllers. Same applies to Tower work... some seem to grasp the problem very quickly whilst others fall by the wayside. Education plays no part - I've seen trainees with 2 University Degrees fail dismally whereas those with far less qualifications have sailed through (I achieved a measly 2 GCE O levels).
Unfortunately no system has yet found a way of sorting "able" from "unable" before they commence training.
Me? Well just say I occasionally see those who trained me still screaming in their strait jackets!