You should be happy for people getting married.
John and Chelsea are getting married and invite Hank, who is under a lot of stress, to the wedding.
Hank wants to come to the wedding and eat at the reception.
Hank puts on a smile and forces himself to congratulate John and Chelsea at the wedding.
Hank comes to the wedding loaded with stress and is in a sour mood the whole time.
John and Chelsea remember that moment and send him a thank you card.
John and Chelsea think that Hank doesn't care about their wedding and are more reluctant to invite him in the future.