An archivist is not just someone who maintains and stores valuable information in a certain manner; archivists also assess whether the given information is worth storing or not.
The information can be provided in the form of photographs, journals, letters, videos, recordings, and so on.
An archivist should make sure that the stored information can be easily found and, later on, understood.
Of course, a specialist would have to have a strong background in history, in order to be able to determine whether the piece is of value or not.
An archivist should understand what the underlying motivations of the creator were and what the intended use of the record was.
If a piece of information is valuable, an archivist would then have to describe and arrange the record.