What life lessons are we taught in the poem "If"?

There are several life lessons taught in Rudyard Kipling's famous poem "If." For, this poem, addressed to Kipling's son, is a paean to the stoicism characteristic of the British of the Victorian Age, and to uprightness.
Stanza 1
In this first stanza, Kipling initially stresses that one must "keep" one's head; that is, remain rational while others are becoming irrational and placing blame upon others rather than accepting responsibility:

If you can keep you head when all about youAre losing theirs and blaming it on you...

Kipling also stresses self-discipline: "trust yourself when all men doubt you." "..wait and not be tired by waiting...."And, he emphasizes manly rectitude: " Or being lied about, don't deal in lies."
Stanza 2
Kipling emphasizes that it is important to dream and have an imagination, but control of one's imagination is necessary, as well, for one must be realistic:

If you can dream--and not make dreams your master...

One must also be strong and willing to take risks and lose, then turn and start again after watching the

...things you gave your life to, broken, and bend down to pick them up and "build'em up with worn-out tools.

Stanza 3
In this stanza Kipling emphasizes fortitude and the ability to begin anew when necessary. A man must be able to suffer losses and start over:

If you can force your heart and nerve and sinewTo serve your turn long after they are gone,And so hold on when there is nothing in youExcept the Will which says to them: "Hold on!"

Stanza 4
This stanza emphasizes and extols the virtues of moral uprightness.  Kipling praises the virtue of humility--"the common touch"--and making the most of time--

...fill the unforgiving minute...with sixty seconds worth of distance won,

Then, he can conquer anything and be a true man.