Q. The job search definitely has a timing/luck component to it. My question is why would an applicant who meets 99% of a very specific criteria outlined by the employer in the posting not even generate an interview? It seems like the hiring manager would only populate the interview pool with these types of candidates.
A. The selection process can be very subjective and luck and timing are always good to have on your side. Many candidates think they meet every aspect of the criteria needed in a posted role, but there may be a host of aspects in your resume which prevent you from being selected. Resume readers are skimmers. They spend less than a minute scanning headlines of a resume unless there is something that attracts their attention to support a few more seconds of investigation. Scan your resume quickly. What stands out? Does it highlight your strengths and experience that match the posting to which you're applying? Make sure your resume format highlights the most important facts on your resume.
Most hiring managers have a prioritized list of desired criteria. You may be missing the 1% which was deemed a must have, and the lack of that item can be considered non-negotiable. Managers also review former employers. The companies you used to work at may be companies the managers respect, or companies they feel do not offer the level of training desired or work atmosphere and culture they want their new hires to have experienced. Perhaps you have short term assignments at more than one company. Many hiring managers scan for "job hoppers" and these candidates can be rejected. If you feel you could be perceived as a "job hopper," organize your resume in a way that emphasizes expertise and skills rather than highlighting a series of short-term positions.
The other areas hiring managers and recruiters use as reasons to screen out candidates include gaps in employment history, typos and too many general statements not showing specific responsibilities or successes. Carefully review your resume to eliminate these issues.
You may have arguments for why none of these should reflect negatively on your candidacy, but people reviewing resumes make quick, subjective decisions when all they have is that resume in front of them. The addition of a cover letter which briefly outlines the strongest examples of the desired experience and the "bonus" benefits of your candidacy - that extra 10% no one else has - can push you from the no interview pile to the top of the must-meet pile. Your luck will increase further if you have a network contact get your resume in front of a hiring manager.
Timing is another issue. Responsiveness will always win. By the time organizations are posting hiring opportunities, they typically have a very serious need for a person to fill that role. Don't assume you can wait a week to respond to an ad, fill out an application or express your interest about an open opportunity. Communicate early, reinforce your interest and thank everyone for every interaction you have.