Sometimes this is true. especially in a situation where everyone
knows everyone else, such as when a company is recruiting internally.
However, this is often not the case. In order for the best person for
the job to win it, a number of very important things need to be in
place (and even then, there’s no guarantee). These include:

The interviewer knows what questions to ask and how to search
for the truthfulness in answers. These two things may sound
simple enough, but I can assure you that a large proportion of
people conducting interviews have received no training, lack
interview experience and often do not even go to the trouble of
preparing for the interview.
The interviewer is not taken in by the charm, good looks, great
humour or any other aspect of the interviewee. This can be a
difficult obstacle, even for experienced interviewers.
The interviewee has learned how to clearly articulate their skills,
key achievements and how they can add value to the organisation.
There is no personality clash between interviewer and interviewee.
Neither party is having a bad day.