What Naruto's Greatest Lessons you have learned that can be applied into your life? 

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The more wood you have, the more successful you will be. Lol xD
Jokes aside.
From Itachi: "Every jutsu has a weak point"
To me: Every problem has a way to be solved.
Itachi also tought me alot about Genjutsu.
You can never trust what your eyes see, as people will try to play tricks on you.