Le pingouin; You nailed it!
Quoting Le pingouin "You need to be able to maintain a good balance of contradictory demands - speed & accuracy, attention to detail without obsessing, flexibility within a rigid framework of rules, confident but aware of your limitations, able to adapt the way you work to suit the situation. "
That is the best description of the attributes required to be an ATC that I have read. For all applicants, study this as it describes just what you will need to do to be successful in the course and role. Brilliant description.
I also agree with Fatty182, on the course itself, very few candidates voluntarily withdraw. Invariably, some are selected who do not have the aptitude for the job and they are not successful in the simulator modules, as they are unable to produce the attributes described by Le pingouin.