For example, he tells of how he had an idea for a story in which the driver of a car pulls into a gas station. After refueling, the driver uses the restroom and on the way out the door he decides to walk around a little since he has been driving north up an interstate highway for hours. He sees a pile of snow melting and all manner of odd things partially buried in the snow. He slips on some snow and falls down an incline. The driver is injured and must wait to be rescued. How this happens depends on several factors: How long before the gas station attendant notices that the driver's car is still parked by a gas pump? If the driver is alone, how long before he misses an appointment with someone in his life? I'm sure you can come up with similar questions. Eventually the state police would be notified and a search conducted. But how long would that take? And what happens to the driver in the meantime?
However, that same situation in a fantasy world is a lot different and it those differences that make writing a good novel much harder. To start, the driver in this example, has to be changed since there are no cars. He can certainly be a traveler on horseback who rides into a small town to rest and who disappears. He might have slipped on snow and ends up hidden in a ditch but if it's the situation you want to keep, then here's a better summary:
A traveler is ambushed by some brigands on the open road. In the fight, the traveler is injured and presumed dead so they roll him into a nearby ditch and take his horse.
Now what happens? There are no agencies to report the missing person as there are in the modern world. In fact there is almost no way for the traveler to be found unless I add lots of details to the world. These details must come from my imagination and must be explained correctly and non-intrusively so the reader understands them and still enjoys the story.
And that's the challenge in fantasy novels. The reader still wants the richness available in the real world but that means knowing thousands of details before you even put pen to paper (or fingers to keyboard). That's what I've done and with luck, I've done a good job too.