Why do you need promotion?

what is promotion ?
deffintion

Promotion involves disseminating information about a product, product line, brand, or company. It is one of the four key aspects of the marketing mix. (The other three elements are product marketing, pricing, place.)
Promotion is generally sub-divided into two parts:
Above the line promotion: Promotion in the media (e.g. TV, radio, newspapers, Internet, Mobile Phones, and, historically, illustrated songs) in which the advertiser pays an advertising agency to place the ad
Below the line promotion: All other promotion. Much of this is intended to be subtle enough for the consumer to be unaware that promotion is taking place. E.g. sponsorship, product placement, endorsements, sales promotion, merchandising, direct mail, personal selling, public relations, trade shows.