I must admit, I would have been very grateful for such sage advice if my father ever gave this advice to me. One cannot be struck by how wise and fitting so much of what the speaker in this poem says. There is definite wisdom in his words, and the speaker clearly shows himself to be somebody who has lived a lot in the world and has a great deal of experience. He has used this experience to shape his morals and values and to work out what, in his opinion, the kind of traits that a man needs to possess in order to be a "man." Consider the following quote:
If you can dream - and not make dreams your master;
If you can think - and not make thoughts your aim;
If you can meet with Triumph and Disaster
And treat those two impostors just the same...
Such lines establish that the speaker has suffered greatly in terms of what he has endured in his life. The fact that he is able to "meet" with both Triumph and Disaster but not be impacted by either in terms of his core personality indicates he has suffered both fame and tragedy in his life and yet still remains undaunted. If my father was able to give such advice because he had experienced such events in his own life, he would automatically be heard because of his character.