The short answer
Postman began in 2012 as Abhinav Asthana's side project, a small HTTP client he put on the Chrome Web Store to fix his own API testing pain. Adoption came from places developers already were, Stack Overflow answers and GitHub, not from marketing spend. Asthana has written that Postman deliberately did not build a sales team early and stood up customer success instead, so the relationship stayed about the user's job rather than a quota. Sales only arrived around 2018, once enterprise demand was already loud, and even then it was triggered by signals like many developers at one company using the tool or a CTO writing in. That sequencing, individual adoption first and the commercial conversation second, is the whole trick.