"If," by Rudyard Kipling, is regarded as his most famous poem. The poem is, essentially, an informative poem. Kipling's poem is meant to teach readers how to be good leaders. Kipling, instead of making a list of the characteristics of good leaders, offers readers examples of what good leaders do.
That said, the poem does offer suggestions about how to be a good leader. One example of this is found in lines nine and ten of stanza two.
If you can dream---and not make dreams your master;
If you can think---and not make thoughts your aim.
Therefore, in these lines, Kipling is suggesting that dreams must never remain dreams. Instead, one must be sure to take their dreams and turn them into realities. By allowing dreams to remain dreams, one can never achieve anything. Dreams are essentially defined as something which one constructs in their mind--either consciously or unconsciously. Without allowing dreams to become a reality, by acting on them, they simply remain something which exists in the brain. If "we" allow dreams to master us, nothing will ever come to fruition. Instead, "we" only continue to dream about our dreams.