No matter how good we are at something, we will bump into somebody who does not agree with us. Maybe they won't agree with our choice, suggestions, ways of working or something else and unfortunately we are not trained well on how to handle disagreements. So if someone disagrees with us, our brain tries to tell us that we are in danger and hence we become defensive.
But, we must reflect why and where these disagreements are coming from. Their negative and positive forms. How are they affecting us and thus react in a more informative way or so, not react at all.