Second-order effects
Etymology
Borrowed from mathematics and systems thinking, where "order" ranks levels of derivation. A first-order effect is the direct result; a second-order effect is the result of that result. "Order" here means rank or degree, from Latin ordo, "a row, an arrangement."
noun · /SEK-und OR-der ih-FEKTS/
The downstream consequences of a consequence — what happens after the obvious first result.
What it names
Why well-intended fixes backfire: the immediate effect is visible, but the effect-of-the-effect is where the trouble hides.
Example
Banning the fee had an obvious first-order win for customers and a nasty second-order effect when the service quietly degraded to compensate.
Related idea
Externalities are one kind of second-order effect — costs that land on people outside the first transaction.