You are confusing selling with advertising.
Advertising tries to pursuade potential buyers that they want to buy product X instead of Y.
Selling is finding out what product the potential buyer wants to buy, and then sell it to them.
Advertising creates the pull-through that good selling can then capitalise on.
i.e. If advertising has convinced the market they need Micro-SD in their phone, you'll have a tough job trying to sell them one without it.