Yes, this is what i have heard and studied. The thing confuses is;

Error #2: Pronoun Errors
Pronoun errors occur when pronouns do not agree in number with the nouns to which they refer. If the noun is singular, the pronoun must be singular. If the noun is plural, however, the pronoun must be plural as well. For example:

Incorrect: Everybody must bring their own lunch.
Correct: Everybody must bring his or her own lunch.
http://grammar.yourdictionary.com/gr...st-common.html

This thing reminded me about the above essay.

Everyone is a singular noun, so should it not be followed by a singular pronoun? As it is said in the above link.