When overloading == in C # there is a practical precedent for overloading! = How is it something other than "return! (A == b);"?

Question

I always wondered why you should overload both; failed to implement !=for the call ==? Is there a reason why you need a "quantum uncertainty equality", if you want to call it this way: a situation in which both x == yand x != yare true, or both false?