Mutually pining is when two people who like or love each other but think the other one isn't interested, making this trope also a sort of unrequited love.
when ur "mutually assured it means that as of now u and the negro next to u knows that ur both packin heat and that he pulled on u u could pull right back on him
the skinnywhite man with a shotgun in his trench coat was mutually assured by the large black man next to him that he was not goin down without a fight
Difficult to define exactly, but it's not the actual *name* of a situation or doctrine. Rather, it describes the outcome of a given action in the circumstances:
In the case of the US and USSR, their shared determination to retaliate to an attack by the other - given the size of their nuclear arsenals - would've assured mutual destruction.