I find this as the struggle as someone who has traditionally worked with large brands. One of the companies I worked with spent millions of dollars on paid advertising while startups and web companies seem to favour inbound marketing a lot more - which big companies aren't really as good at (or pay as much attention too.)

> 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 marketing.

and figuring out that particular viral loop in the product isn't easy. It takes lots of efforts from a marketer as well as an engineer to find out that one thing or pain point from which you get growth.