If natural language conditionals were understood in the same way, that would mean that the sentence "If the Nazis had won World War Two, everybody would be happy" is vacuously true.
Given that such problematic consequences follow from a seemingly correct assumption about logic, they are called paradoxes.
They demonstrate a mismatch between classical logic and robust intuitions about meaning and reasoning.
In natural language, an instance of the paradox of entailment arises: And Therefore This arises from the principle of explosion, a law of classical logic stating that inconsistent premises always make an argument valid; that is, inconsistent premises imply any conclusion at all.
This seems paradoxical because although the above is a logically valid argument, it is not sound (not all of its premises are true).
For example, the following are valid inferences: but mapping these back to English sentences using "if" gives paradoxes.
Again, under this interpretation both clauses of the conclusion may be false (for instance in a series circuit, with a light that comes on only when both switches are closed).