Overly Attached - Know when to let go of emotional attachment to your work

Recently, I encountered this problem while collaborating with a smart, senior engineer who couldn't make logical decisions if it meant deprecating the system he and his team had worked on for a number of years. Even though the best thing would have been to help another team create the replacement system, they didn't want to entertain the idea because it would mean putting an end to something they had invested so much in.