Secret here: every story is different.
In my first start-up, it was pure hustle. We had a concentrated number of high dollar customers, so I did “outbound”. I found the right decision makers, got on the phone, got on a jet, and set up the meetings.
The second time at EchoSign, I tried pure hustle in the beginning — but it failed for us this time. What worked in the end was creating a small in-bound stream from press and PR (TechCrunch on launch, and then a steady stream of events, press, etc) and partnerships/API/integrations. This was a slower way to start, but it built more customers. By number.
I meet founders that get their first 10 customers with outbound. With inbound. With content marketing. With their friends at YC/etc. And a combination of all of the above.
In the end, we try everything, and we tend to get our first 10 or 20 customers based on what we do the “least worst” in customer acquisition.