Up to 70 percent of the applicants will not become certified. Generally, applicants do not succeed because they do not have the intense focus that it takes to perform the job. That's one of the things that an interviewer is going to be watching for, so don't get distracted and start zoning out looking at the nameplate on his desk. If you can't look him in the eyes for half an hour, he's going to assume that the planes under your watch might receive a similar amount of attention. Also, the test is extremely difficult. Lots of flash cards and determination will help you become certified.