Answer: The friends want to act with the intention of in order to bestow and so you can humiliate yourself before them and thus adhere to them, connect to them, and get close to them spiritually. Therefore, you should humble yourself before them.
But if you try to humble yourself before other people, then with regard to what do you humble yourself? Do you do so with regard to their corporeal desires and egoistic goals? They don’t operate towards the direction of the spiritual goal. When you annul yourself before a friend, it helps the two of you since you are serving as an example for him. If he is your friend along the spiritual path, then he will understand you correctly. He will see that you are working on self-annulment, on bestowal, and that you are giving him an example. This means that your action of self-annulment is correct in every sense: both towards the one who performs it and the one who sees it.
But if you behave that way with regard to a stranger, he will think that he is greater if you lower yourself before him, and he will take pride in it and his ego will begin to grow. He may also not understand why you are suddenly ingratiating yourself before him and would think that you want to deceive and to use him. From all these examples, we see that it’s only before a friend along the spiritual path who will understand me that my annulment can be beneficial for both of us.
From the 1st part of the Daily Kabbalah Lesson 2/7/13, Writings of Baal HaSulam