* Formal: Despite his years of experience, the detective knew that even the most meticulous investigation was not infallible.
* Informal: No one is infallible, even the best athletes make mistakes sometimes.
* Humorous: My cat thinks she's infallible at catching laser pointers, but she's always one step behind.
* Philosophical: The pursuit of absolute knowledge is a fool's errand, as no human being can be infallible.