Your code is not you.

Imagine the following scenarios:

Team Member1: "Hey Team Member2, your code is not working.. I could not integrate my code now"
Team Member2: "No, buddy. It was working alright. Why don't you double check yours?"
Team Member1: "I did. Looks like you are assuming that the object I passed will not be null. That's not the case."
Team Member2: "I ran my tests. It's working fine."
Team Member1: "But it's not working now. I did not change your code! Come on."
....
....
....

Team Member2: "No Man! I can't change anything. It works fine for me."

Now it's no more a technical issue. It's status quo. Solving this is going to take time and energy of more than just Members 1 & 2. What could have been different if:

1) Team Member2 knew that his code is not him and also when to lose the ego. It's an application he/she wrote which nothing but a set of instructions for the computer to perform.

2) TeamMember1 just knew when to replace 'your code is not working' with something like 'Looks like WE have got an issue to solve'.