The marketing planning (concretized in the marketing plan) is an essential organizational activity, considering the hostile and complex competitive business environment. Our ability and skills to perform profitable sales are affected by hundreds of internal and external factors that interact in a difficult way to evaluate. A marketing manager must understand and build an image upon these variables and their interactions, and must take rational decisions.
What was the outcome? As much as 90% businesses started by entrepreneurs and small business went busted or failed within a year. I experienced one of the many busts few years ago (with my cafe business) because i don't really have a proper and "the few solid sheets" called a marketing plan.