“Your teen may be weaker, but he is not without the ability to do himself and others a lot of harm by showing you that you can't control him at school or anywhere else when he is out of your sight…. [W]hen he is on his own, your only control over him is the strength of your relationship.”
Source: Unhappy Teenagers A Way for Parents and Teachers to Reach Them (2002), p.9
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William Glasser 14
American psychiatrist 1925–2013Related quotes
“If you can't control your peanut butter, you can't expect to control your life.”
Source: The Authoritative Calvin and Hobbes: A Calvin and Hobbes Treasury

"If his forces are united, separate them" is also interpreted: "If sovereign and subject are in accord, put division between them."
Source: The Art of War, Chapter I · Detail Assessment and Planning

The origins of this quote are unknown. At least two sources can be traced back, but these sources date back to the 1940 years; long time after Lincon's death.
Source 1: The 2003 "Masonic Historiology" from Allotter J. McKowe contains on page 55 (page 55 is dated on Jan. 11, 1944) the poem " What Is a Boy? http://books.google.de/books?id=K5CHWRttt-gC&pg=PA55&dq=desk" from an unknown author. The poem reads:
:: He is a person who is going to carry on what you have started.
:: He is to sit right where you are sitting and attend when you are gone to those things you think are so important.
:: You may adopt all the policies you please, but how they will be carried out depends on him.
:: Even if you make leagues and treaties, he will have to manage them.
:: He is going to sit at your desk in the Senate, and occupy your place on the Supreme Bench.
:: He will assume control of your cities, states and nations.
:: He is going to move in and take over your prisons, churches, schools, universities and corporations.
:: All your work is going to be judged and praised or condemned by him.
:: Your reputation and your future are in his hands.
:: All you work is for him, and the fate of the nations and of humanity is in his hands. Quotes about life http://www.quotesaboutlifee.com/2012/04/best-quotes-on-life-best-sayings-on.html
:: So it might be well to pay him some attention.
Source 2: The newspaper "The Florence Times" from Florence, Alabama (Volume 72 - Number 120) contains in its Wednesday afternoon edition from October 30, 1940 a statement from a Dr. Frank Crane. The entitled "What is a Boy?" statement http://news.google.com/newspapers?nid=1842&dat=19401030&id=yx8sAAAAIBAJ&sjid=I7oEAAAAIBAJ&pg=3738,3720511 reads:
Disputed

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 601.
“You can only control your own actions. Not other people’s reactions.”
Source: Something Blue

[Baqir Sharīf al-Qurashi, The life of Imam Muhammad al-Jawad, Wonderful Maxims and Arts, 2005]

“Do not kill your ego and do not let your ego to kill you. Control your ego and rule over it.”
Flow of Divine Guidance (vol.1)

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 435.