Learn Spanish (Latin America): Mucha gente cree que se volvió loco y paranoico. - A lot of people believe that he became crazy and paranoid.

In Spanish, volverse is used for profound, involuntary changes in someone's personality, mental state, or character—like going crazy (loco) or paranoid (paranoico). You would use hacerse when the change involves deliberate effort or personal evolution, such as becoming a doctor or getting rich.

Could we use se puso instead of se volvió in this sentence?

Not quite. Ponerse is generally used for temporary, passing changes in mood or physical appearance (like becoming sad, nervous, or turning red). Because becoming crazy and paranoid implies a deep, lasting psychological transformation, volverse is the correct choice.

Why is the verb cree in the singular when 'a lot of people' means more than one person?

In Spanish, the word for people (la gente) is a collective noun that is always grammatically singular and feminine. Because of this, it must take the singular adjective mucha and the singular verb cree.

Why does cree que trigger the indicative (se volvió) instead of the subjunctive?