A tidy little proverb in rhyme: if there's a cure, find it; if there isn't, let it go. More a piece of homespun philosophy than a story, and better suited to slightly older children.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
For every evil under the sun
There is a remedy or there is none.
If there be one, seek till you find it;
If there be none, never mind it.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition