unforeseen consequence
noun phraseUK /ˌʌnfəˈsiːn ˈkɒnsɪkwəns/
US /ˌʌnfərˈsiːn ˈkɑːnsəkwens/
A bad thing that happens later because of something you did, even though you did not expect it.
The new road made traffic faster, but an unforeseen consequence was that the nearby park became very noisy.
RELATED WORDS
OTHER MEANINGS
2. A good result that nobody planned or predicted.
An unforeseen consequence of the school garden was that kids started eating more vegetables.
3. A problem that appears much later than the action that caused it.
Years later, the unforeseen consequence of cutting down the trees was that the soil washed away.
4. Something that happens in a story that the characters did not expect.
In the book, the hero's wish had an unforeseen consequence that changed the whole town.