What’s the difference between “its” and “it’s”

Read the excerpt from "the love song of j. alfred prufrock." and indeed there will be time to wonder, “do i dare? ” and, “do i dare? ” time to turn back and descend the stair, with a bald spot in the middle of my hair— [they will say: “how his hair is growing thin! ”] my morning coat, my collar mounting firmly to the chin, my necktie rich and modest, but asserted by a simple pin— [they will say: “but how his arms and legs are thin! ”] do i dare disturb the universe? in a minute there is time for decisions and revisions which a minute will reverse. which lines indicate that the speaker is concerned about what others think of him?