Dragons weren't exclusive to the Mortal Plane. As one of the most ancient species, dragons can be found in countless dimensions all across the universe. Since the dragons in the Mortal Plane intentionally stay away from humans in the current age, it would actually be easier to meet with dragons in other dimensions.
There were all sorts of myths and stories about what would happen if a human met a dragon. The end result would typically be that the main character would receive numerous benefits, such as high-quality weapons, the glory of slaying a dragon, dragonblood baptism, the beginning of a epic quest, and so on.
In fact in knight novels the main character would always meet a dragon, and then use the dragon as a stepping stone to greater glory... those characters typically joined the ranks of harem protagonists among clichés.
But for any normal adventurer who was traveling solo, meeting one of these big lizards would doubtlessly be nothing but misfortune.
