I worked with a guy who was really grumpy and would go home sick (a lot), if he had to do something on the second floor (it was an old time telephone switching office).
Finally, out of desperation to get something done, I wrote a note to his boss telling him how hard working, helpful and knowledgeable this guy was. The boss showed it to him. After that he became absolutely professional, helpful and even friendly. It was a miraculous change.
I happened to meet him several months later at a company meeting and he thanked me for the letter I wrote. I think he just needed some kindness for his weary soul. – Debra 😀