General terms:
* Paradox: A seemingly self-contradictory statement that may nonetheless be true.
* Irony: A situation where the outcome is the opposite of what is intended or expected.
* Reversal: A change in the direction or course of something, often resulting in the opposite outcome.
* Contingency: An event that could happen but is not expected.
* Unexpected: Something that is not anticipated or predicted.
More specific terms:
* Backfire: When an action intended to achieve a certain outcome has the opposite effect.
* Counterintuitive: Something that goes against what seems logical or expected.
* Reverse psychology: A technique used to persuade someone to do something by suggesting the opposite of what you want them to do.
* Unforeseen consequences: Unintended outcomes that result from an action.
The best term to use will depend on the specific situation.
For example, if you are talking about a situation where someone tries to be funny but ends up offending people, you might use the word "irony" or "backfire." If you are talking about a scientific experiment where the results are unexpected, you might use the word "paradox" or "counterintuitive."