Back in grade school, some teacher probably had you do an exercise where you separated fact from opinion. "This picture is beautiful" is an opinion. "Barack Obama was born in America" is a fact. These days, according to Dunning, more and more of us are forgetting this essential distinction. If you want to be a little smarter, you need to remind yourself that some questions aren't open for personal interpretation.
Source : https://www.inc.com/jessica-stillman/top-stupidity-researcher-do-these-5-things-to-be-instantly-smarter.html