In the field of psychology, the Dunning–Kruger effect is a cognitive bias in which people of low ability have illusory superiority and mistakenly assess their cognitive ability as greater than it is. The cognitive bias of illusory superiority comes from the inability of low-ability people to recognize their lack of ability. Without the self-awareness of metacognition, low-ability people cannot objectively evaluate their competence or incompetence. http://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect
For those unfamiliar with percentile rankings, briefly….
Say you get 95% of questions right in a test — sounds good. But if everyone else does, then your performance is actually average. Percentiles are a method of marking, which ranks your score COMPARATIVE to other scores within a population. If you rank at the 10th percentile, 10 percent of all scores, in the population tested, fall BELOW you. If you rank at the 90th percentile, 90 percent of all test results fall BELOW you — you’ve made it to the top 10. 50% is dead on average. Bizarrely, in a tendency which has been termed the ‘above-average effect’, it seems most people — no matter what their competence/ability — perceive themselves as above average, hovering around the 60th percentile.
Generally, you might also find the communication with someone who works in psychology interesting.