One reason is because they have survived. A fresh graduate, or a one-year-in second jobber could be a genius with encyclopaedic knowledge of the subject. They

One reason is because they have survived. A fresh graduate, or a one-year-in second jobber could be a genius with encyclopaedic knowledge of the subject. They could also be utterly incapable of doing the job. Their Dunning-Kruger overconfidence is untempered by the experience of being overtaken by considerably more competent cow-orkers. Someone who has been at it for 5 or more years, should have a reasonable grasp of whether or not they can do the job (though not necessarily the level at which they can do it).