I was visiting Sa Pa, Vietnam, and navigating with Organic Maps. I was looking for a street that would bring me back to the city center. I could not see any on OSM or Google Maps. I walked for a while and was able to see a street that led in the right direction. It turns out that it connected to another street that brought me where I wanted to go. This made me realize how much of the useful information in maps depends on people walking, running, or commuting through those streets. You cannot see these kinds of streets from satellite images. You can only know them, but knowing them, you may not use GPS tracking to record them. I think this leaves only runners and anyone who likes walking to discover most of the streets that are not currently on the map.