It is easy to look at something you created or implemented with blinders on. You put the effort into it and figured it all out and now someone else (a new manager or vendor, etc.) is coming to you saying that their idea is better and will improve upon what you built. It is human nature to be skeptical and defensive, especially since people are always over-promising and under-delivering on what they initially say they can do.
The big question here is were you receptive or did you immediately defend what you are already doing? Are you keeping an open-mind in order to evolve or are you a brick wall and its your way or the highway?