Let’s call him Bob.
At the coffee machine Bob asks: “Do you have a moment? It’s important.” You find an empty office and close the door.
Bob: “I’m leaving.”
How do you react?
Option 1: Be Resentful
Get angry on the inside. Show defensiveness. Interrogate Bob why he’s leaving, where he’s going, what’s wrong with our place etc. Bob feels your resentfulness and starts to feel like he’s wronged you.
During Bob’s remaining time your work relationship suffers. At the end you shake hands, thank Bob for his contributions, and part ways.
Option 2: Be Positive
Let it sink in for a moment, suppress the negative reactions it triggers inside of you. Instead, be positive and congratulate Bob! He has taken a big leap and mustered the courage to tell you. Show genuine interest in their future plans without being interrogative. Bob should feel good about telling you.
During Bob’s remaining time he proactively helps the transition: training colleagues, sharing knowledge and finishing work-in-progress. At the end you throw a party, have some beers and recall office war stories.
I don’t need to tell you which option you should be choosing. This is the last impression you’ll make before Bob leaves: if you part in a positive way, something good may come of it in the future. You want Bob to speak highly of you and your company after he’s left (especially after he left). He might be a future customer, co-worker or manager. Nothing good comes from resentment.