What are the primary and secondary objectives of advertising?

The primary objective of advertising is to sell something, anything.

The secondary objective of advertising is to sell more of that something.

Secondary advertising can also mean the visualization of that product in use, again with the objective of selling more. Two examples:

Toothpaste ad. Research shows that a pea-size glob of toothpaste is sufficient for proper dental care. The toothpaste ad shows a huge double-layer glob, enough for a week of brushing.

Shampoo ad. Directions say wash, rinse, wash again. That second washing is a waste of shampoo and water unless you've been soaking your hair in used motor oil all day. And some shampoo ads tell you "to get your hair REALLY clean" [and who wouldn't? - they've got you there!] wash & rinse a third time!