A term expressing an expectation of reciprocity. If event A happens, then event B will certainly follow. Most commonly used in the phrase "mutually assured destruction," which posits that the best defense against a nuclear-based attack is the threat of a "mutually assured" retaliatory nuclear-based attack...although the term can be applied to events less earth-shakingly catastrophic.

to feel safe because others feel the same way
peer support
feel the same as someone