In Thinia:
Many powerful heroes and villains have lived and died across the history of Thinia. These indiviudals are exceedingly rare. Some examples of such exceptional people include Lander the Great, Khan Vondrad, Sigrun the Valkyrie, and Empress Saelphira Dawn. More often than not these exceptional individuals meet unexpected and tragic ends due to betrayal, wearines, or their own flaws.
Even powerful spellcasters and accomplished warriors rarely rise to levels where they are able to combat the more dangerous monsters of Thinia. For this reason there are still parts of the world where Dragons, Giants, Demons, Angels, Undead, Aberations, and other powerful and terrifying creatures lurk. Many adventurers begin their careers with dreams of slaying dragons and reaching the heights of mortal capabilities, but very few succeed. Most adventurers die on quests or retire after achieving whatever goal set them on the path to adventure in the first place.
Still, some individuals rise quickly to great power and believe themselves to be invincible. But many powerful individuals have met misfortune after insulting a physically weak noble with a loyal army. A wizard may be able to incinerate a dozen charging soldiers with a fireball, but one hundred commoners with bows will quickly overwhelm even experienced and powerful people.
In Game:
Put another way, there are very few individuals above level 15 in Thinia. When commoners refer to powerful spellcasters or warriors they are likely refering to people who would be the equivalent of level 10 and above adventurers. If adventurers do make it into tier 3 (11-15) or 4 play (16-20) they are extremely exceptional. But even at these levels they are still singular people. Characters/Adventurers in D&D are not gods or unkillable at higher levels. In fact a level 20 character could quickly be killed by an army of commoners under the right or wrong circumstances.
As such, adventurers should always consider the resources available to those they interact with. Nobles, gang bosses, monarchs, priests, and many others can direct dozens or hundreds of enemies against adventurers if antagonized.
