Fill in the blank: There can be many timeline events associated with a contact, but a timeline event cannot be associated with ____ contacts.

A timeline event must be associated with at least one contact so HubSpot knows where to display the activity. HubSpot can associate the event through a contact email, contact vid, or another supported identifier. Without a contact association, the event cannot appear on a contact timeline. This requirement keeps timeline activity tied to a specific CRM record. Other associations may add context, but they do not remove the need for a valid contact link.