This should be a given for any profession. Just because we are designers this should not be any exception. Those who do such a thing would not go into a doctor or lawyer, and tell them how to do their job.
Recently after question a person about their design choices I was belittled. Because you and me both know we only want the best for them design wise. The situation taught me that you have to let them see the big picture. Even other times there are clients who don’t want good design.
You may say clients don’t want good design? Well more so it may be the end result of the project. Because even though you see beautiful design work on instagram, dribble, behance and etc it would not work. By not working it will not work for an actual client. But at times that may be different.
Therefore in regards to some belittling your expertise focus on the clients that matter. Do not let yourself get worked up by someone who does not appreciate your advice.