Thats not entirely true. You can't build car, paved roads, load capacity in one go, you got to make the first horse cart without the horse.. and many would object saying horse is literally free, why should i pay for fuel. where would i refuel wheres the horse can feed itself. horse can drive itself if necessary etc..
There is no single formula for success. Sometimes you are too early and you fail. Snake oil startups are getting billion dollar valuations while a legitimate idea may be rotting in another corner of the world. It's a combination of lot of things. Sometimes I feel many of the yc companies are successful not because people are jumping to buy the license, but because they have a network effect and are vetted by a community and perceive it as the better option while it may not be such. Connections, Money, Advices, Talent, Idea, Marketing, Sales, Management - every single thing is part of the puzzle.
Somtimes you are lucky to get the market fit right of the bat, but many times you have to try hard and struggle a lot before you even have a chance to have a glimpse of market fit. In the case of the author of the blog, if he had build a hype around his product like this is the next biggest thing and got a network effect going (your peer doctors are using it) it may have turned out way different. He wouldn't need to charge it initially or have a free plan that is good enough to get them hooked etc. Don't know there are thousands of variations possible. He simply stopped too early IMO.