Marketing is important, however more important is to build in a viral loop into your product, that for every new customer x>1 new customers are contacted.

This is how social networks work, invite your friends systems, etc.

However, even then marketing is still important. But too often marketing is seen as: Spend huge amount of money on ads.

No: marketing is market research, choosing your target audience, branding, image building, tone-of-voice etc.