Why...I had no real idea what the job entailed before starting at the college. I had no idea there was different disciplines within ATC, I'd never heard of the ANO, Air Pilot or MATS. I could tell a 747 and Concorde part and that was about it.
I passed everything, validated and have been an OJTI for nearly 2 years. Didn't do me any harm, I just had to work a bit harder to catch up.