's "If" is a poem that discusses manhood, leadership, manners, and perseverance. It's as if he gives the next generation tips on how to manage the vicissitudes of life and keep one's sanity and reputation intact. Life is full of different voices urging us to go one way and then another, ups and downs, and successes and failures. The lines in question discuss how a person should handle success versus failure and/or a crisis.
"If you can meet with Triumph and Disaster
And treat those two impostors just the same. . . (Lines 11-12).
The idea within these lines is that each person will face victory and defeat as well as success and crisis in life, but Kipling calls these things imposters. Often we are fooled by labels. We are fooled by other people's perceptions about us, or we can be fooled by the labels and perceptions we have about ourselves. The advice suggests that if we humbly take a triumph and a disaster as learning opportunities, rather than succumb to selfish feelings about either one of them, we will enjoy life more fully and in a more authentic way.