This famous advisory poem by Rudyard Kipling is, in actuality, a single run-on sentence. That makes it rather difficult to usefully summarize the stanzas without referring forward always to the final stanza, which expresses the outcome of what will happen if all the preceding advice is followed. If all the advice given is followed by the reader, "the earth and everything that's in it" will be yours, and "you'll be a man, my son."
Bearing in mind always, then, that each stanza is suggesting ways to ultimately be a man, the first stanza advises keeping a clear head and trusting oneself, even when others don't, without blaming people for doubting you. It advises patience and not responding to lies with lies or hatred with hatred.
The second stanza advises being able to dream and think freely without becoming obsessed by one's dreams or thoughts and pulled away from practical things. Triumph and disaster should be treated the same: that is, responded to with a clear head. Things we spend time on...
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