Other than an unfortunate event, when you do not hear back from the perfect candidate, it's perfectly clear that this is not the job for him. Interested applicants typically contact a potential employer within a day or two. If a week passes without a word, then actions have spoken louder than words.
Any number of factors can cause solid applicants to leave wistful employers in the lurch. For example, on the morning after, perhaps the job did not look as enticing as it appeared during the interview. It is also possible that his current employer made him an offer he could not refuse. Or, perhaps he was just being polite. Sometimes interviewers oversell a company, and when applicants do some checking around, such as with their friends or even on the Internet, their enthusiasm can be extinguished.
Nonetheless, when an applicant opts out, you should consider yourself lucky. If a candidate takes himself or herself out of contention, you and the candidate both win. Although you may not want to conduct more job interviews, it definitely beats the prospect of conducting more exit interviews.
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