Why is there so much mediocrity?

Lucy Kellaway:

Two years ago I graduated from Oxford university with a 2:1 in philosophy, politics and economics. After a year of looking for a job, I was hired by a large and very well-known business. At first I was in awe, but now I’ve discovered something that surprises and depresses me. Most of my colleagues are neither terribly bright nor terribly hardworking. As this is my first experience of corporate life I’m puzzled and want to know – is it me? Is it them? Am I missing something? I just don’t get it; if these companies are so hard to get into, how come most of the people who have made it are so mediocre?

Graduate trainee, male, 24