I don't exactly understand why my while loop is not catching any of these conditions

I’m trying to output the input string in reverse and when the user inputs "done", "Done", or "d" it will stop. With this, the while loop does not catch any of these conditions to stop the loop.

#include`<iostream>
using namespace std;

int main() {

   string userInput;
   int i;
   char output;
   getline(cin, userInput);

    
    
      while (userInput != "done" || userInput != "Done" || userInput != "d") {
        for (i = userInput.size() - 1; i >= 0; --i) {
            output = userInput.at(i);
            cout << output;
        }
        cout << endl;
        getline(cin, userInput);
    } 
   

   return 0;
}

>Solution :

replace

while (userInput != "done" || userInput != "Done" || userInput != "d")

with

while ( ! (userInput == "done" || userInput == "Done" || userInput == "d") )