The Mishna in Avos (4;10) says "a person should be exceedingly humble in front of every person."

The Rambam explains that no matter who we are speaking or dealing with we should relate to them as being more honorable than us. When we treat everyone in such a way it allows for us to acquire the trait of humility.

The Sforno explains the mishna by stressing the mention of before everyone. If a person does a true introspection he will undoubtedly realize the many character flaws and problems he has. In his own eyes and heart he knows that he is very far from perfect. But as soon as this person goes out and interacts with other people he carries himself as if he is in fact perfect without flaws. The mishna is therefore telling us that just as you know inside all of your faults you shouldn't project to others when you are in front of everyone that you are perfect. The same mind set you have internally should be projected outward as well.

Shabbat Shalom,

Heath