Look at these examples:
Chacun a son billet?Does everyone have their ticket?
Il faut toujours avoir sa carte sur soi.One must always have one's map on them.
You must always have your map on you.
Personne n'a ses clés ?Does nobody have their keys ?
Tout le monde a son opinion.Everyone's got their (own) opinion.
Note that when expressing possession with indefinite pronouns (personne, tout le monde, chacun/e) and impersonal expressions such as il faut, you will use the possessive adjectives son, sa or ses (its/one's here).
Remember that possessive adjectives agree in gender and number with the *owned* item (son billet / sa carte / ses parents).
See Common mistakes with mon/ma/mes, ton/ta/tes and son/sa/ses (French Possessive Adjectives)
ATTENTION: You never use notre/nos (our), nor votre/vos (your)
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