If we had to describe the sound of this poem in three words, they would be: "run-on sentence." Okay, so that's a little harsh, but if you think about how run-on sentences work, you'll see what we mean. If you've ever encountered a run-on sentence, you know they tend to go on and on and on, like this, "So I went to the store, and then I went to McDonald's, and I got a cheeseburger, and then I had a Diet Coke, omg I went to the pet store next, and… and… and…"
So, maybe "If' doesn't quite sound like that, but then again it sort of does. The most widely-used literary technique in this poem is anaphora, which is the repetition of the same word, or series of words, at the beginning of successive lines. More than anything else, it is the anaphora in this poem that gives it a run-on feel. Take a peek at lines 9-11,
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
Notice all of those phrases: "If you can," "If you can," "If you can." Anaphora goes down in lines 18-20 as well:
And risk it on one turn of pitch-and-toss,
And lose, and start again at your beginnings,
And never breathe a word about your loss: (18-20)
Part of the reason the poem is so repetitive, and sounds so much like a run-on is because it's a poem spoken by a father to a son. Repetition works well on kids, especially if you're trying to teach them something. While at times all the anaphora—the "if, if, if" and the "and, and, and"—gets a little tedious, but if you were trying to give a young person a mini-lecture about how to become a man and conquer the world, you might resort to this strategy, too.