How to deal with challenging colleagues?
On listening to some other aspects of the problem, i suggested some solutions approach him, which he may take forward. But this kind of situation happens to most of us, even though the colleagues, counterpart, or partner also has equal power.
In my opinion, the first step would be how do you think of yourself to others sets the direction in dealing with colleagues successfully.
We have choices of how we look at ourselves with the counterpart. Do we look at our position as equal to others or inferior, or considering the task importance or goals, do we look at ourselves as an overall lead? This feeling comes from the responsibility we assume for the overall organizational goal. When we urge for a higher purpose, that will push us to think beyond our current position. That feeling or thinking itself puts you on a higher level compared to your colleagues.
For example, in the above instances, when the person thinks of himself as he is ultimately responsible for overall delivery (which is usually the responsibility of the business head), that responsibility assumption will make him feel he is equal or more powerful than his colleague.
When we assume higher responsibility even at the mindset level, that will change our perception about ourselves relative to other counterparts.
Most of the time, we are not failing during the conversation or in an argument, but before we initiate the conversation, we lose ourselves with the self-image.
You could have observed that some people may be with less experience, age, or relatively less positional title but move across any function or level to make things happen. They put the organizational goal or higher purpose in front of them than any other positional power.
Just relate yourself.