Many people think, that 90% of mankind are stupid. These people, who think so, always count themselves into the 10 remaining percent.
Following this line of thought, everybody, when asked, will be sure to belong to the 10% of intelligent people. The remaining 90% seem not to exist at all.
Mankind therefore consits of only 10% of itself. This means that all mankind is of high intelligence and the overpopulation of earth is no problem at all.
As if that wasn't clear from the very beginning.