Which is correct: "everyone's life" or "everyone's lives"?
I know that when the pronoun everyone is used as a subject, it takes singular verb agreement (as in the sentence "Everyone was there"). But this by itself doesn't seem to show that the possessive form "everyone's" always acts like a singular possessive noun.
An example of the reverse situation: when the "singular they" is used as a subject, it takes plural agreement, but the possessive form their can be followed by a singular noun. So the verb agreement that a pronoun takes isn't always the same as the grammatical number of a noun after the possessive forms of the pronoun.