The short answer
Brian Halligan and Dharmesh Shah started from an observation, not a product: buyers were finding answers on blogs, forums and search engines long before a salesperson showed up, while companies were still cold calling. They named that shift inbound marketing, then built HubSpot as the tooling for it, so the content that acquired their customers was also the proof that the method worked. The second decision mattered as much: against investor pressure to chase enterprise, they served small and medium businesses, which was a blue ocean while everyone else fought over the same large accounts. Pricing moved from an arbitrary 250 dollars a month to a two axis model on features and contacts, so revenue grew as the customer grew. Then, six months before IPO, they gave away a free CRM, which is the same move again: offer value before capturing it.