A small, primitive village has yet to discover fire, which is a good thing because there are highly flammable (but not otherwise dangerous) gasses in the air. The heroes, blissful in their ignorance, don't know that and think it a wonderful idea to show the locals open flame.
Unbeknownest to the character, he is in the royal bllodline. Suddenly the majority of royals fall ill and die, and the hero is left with the crown, but no experience or idea of what to do.
A Deity of some sort has unleashed a plague of bookworms or something like that in the area. Almost all spellbooks are destroyed, along with bardic and historical books.
For those familiar with cantrips, you know they are minor acts of magic that have hardly any noticable effect on the world. For example a cantrip to make your food taste better won't heal you any more, or be any more nourishing, just won't make it so hard to get it down. A light cantrip certainly won't be able to blind or even distract anybody, but you might be able flash it to signal someone looking at the right spot.
What if children's nusery ryhmes were a form of cantrip? Like the "Rain, Rain, go away, come again another day." One child singing it wouldn't do more than spare her house a couple raindrops, but what if the whole village got together and was chanting in unison? Each one doing just a bit might actually be able to divert a whole storm...