Guide _ in a marketing you will think, record and document all your ideas, products and services offering, price, distribution channel, programs, sales direction, customer segment and so on. I have experienced whereby I suddenly realized that my business is not going on the right direction because I didn't follow my marketing plan. Have you experienced that? Or perhaps you suddenly realized that the thing you do know supposed to be done many months ago because you forgot about it? And you forgot because you don't jot it down and plan for it? This is what I mean that marketing plan as a guide. I cover this in my Marketing Plan Breakthrough S6PEC.
When I ask entrepreneurs and small business owners, it is not unusual for not having any marketing plan. I once read that Sir Richard Branson never had any marketing plan when he started the 1st Virgin business many years ago. In fact in one study of entrepreneurship (I couldn't recall the name of the study) was that as much as 50% of entrepreneurs and business owners don't have a business plan and marketing plan when they first started the business.