It was when I was in b-school that I realized that marketing is the most important function in a business. Finance and human resources are important, but come later, once you have a business and people. Product development and operations seem more fundamental, but think about it: until you think of the customer, of who you’re making the product (or providing the service) for, you haven’t got much of a business. And that, that thinking of the person who’s going to pay you for doing what you do, and thinking of how you are going to get them to buy what you have to sell, how you make the product better so they want to buy it: that’s marketing.
And when you put it that way, it’s what you start doing before you set up a business and hire people; before you start working on that marvelous new software idea you have. It starts when you say, “Oh, this will be a great concept, and this product is going to help people do that.”