If the product is really great people will use it but good marketing takes that effect and amplifies it. Marketing is about telling a story and creating a sense of values, benefits and identity around the product. If people don't _try_ your product it doesn't matter how good it is. If people don't _care_ about your product they might well use it all the time but never tell anyone.

I'll leave you with two quotes, the first is uplifting and the second a bit of an eye-opener:

"Product is the value, marketing is a multiplier."

"Nothing Kills A Bad Product Faster Than Good Advertising"