Not only was Rabbi Israel [Salanter] opposed to the performance of the finer points of mitzvot at the expense of human beings, he held that one had no right even to perform the essentials of a mitzvah or even extricate himself from grievous sin if he thereby inflicted suffering on someone else.
A question was submitted to him: Someone had sinned in secret against a friend of his by speaking evil of him. Was it permissible for this person now to go to his friend and seek forgiveness? In so doing, however, he would have to disclose what he had said to the friend he had maligned.
Rabbi Israel [Salanter] ruled, that although the questioner would absolve himself from grievous guilt by seeking his friends forgiveness, he had no right to pursue his own good by hurting his friend - enhancing his righteousness at the expense of causing distress to someone else. This is the extent to which R. Israel took the feelings of others into account, how he engaged in complicated calculations so as to avoid giving any hurt or distress to others. -- The Mussar Movement, Volume 1, Part 2 pages 229 - 230
Humility can display itself in many forms. It can be the simple deference we show to someone else, or the more rigorous steps we take not to cause offense or be callous to someone's feelings and reputation. Humility is nothing short of a thoughtful middah. It is unimaginable how many wars could have been avoided if the behavior above was modeled.
not higher, not lower
Our Mashiach modeled this principle so well:
"The greatest among you shall be to you as a servant. Everyone who lifts himself up will be brought low, but everyone who lowers himself will be lifted up." -- Matthew 23:11-12, DHE
As soon as we think we are above someone else, we have lowered ourselves out of default. One cannot be high at the expense of others; on the contrary, the raising of oneself is only a means to a lesser reputation and a lesser resemblance of the character of our Mashiach. When we take control over what we say because we care how it affects others, then we are truly being disciples of the Messiah.