They don't self disqualify, they think because they didn't get position X in company Y they aren't good enough. When in actuality, position X in company Y was given to the friend of the son of the manager doing the hiring. Intelligent people may be intelligent as far as abstract pattern recognition, but it is incredibly difficult to get jobs without some level of networking. A lot of intelligent people assume because, in High School and to a certain college, people got put into classes based on merit that this applies to the real world. While it is true that actually being good at your job will make it easier to get said job, the nepotism and networking involved is far far more important. They then have their fancy degree and their proud valedictorian sash and apply to all the places they want to work, usually in incredibly over saturated fields (made worse by the fact that, now that so many people are getting college degrees, it isn't a bonus but a necessity), they don't get any jobs in the field they want. The obvious conclusion to come to is then "If the system hires people based on merit, and I am not getting hired, then I do not have merit." Then, the obvious conclusion is to get a job elsewhere.
This all precludes the fact that all middle class college graduates can't survive off daddy's money to go through unpaid internships to network, nor can daddy tell his underling to hire his sweet daughter to that programming position.