“If we will repeatedly suffer the humiliation of admitting that we really do not know what we're talking about, eventually we will.”

Variant: and it ought to make us feel ashamed when we talk like we know what we're talking about when we talk about love.
Source: What We Talk About When We Talk About Love

When asked by a radio DJ if One Direction calls "dibs" on girls (26 June 2012) https://www.youtube.com/watch?v=LV85tICyfEA&t=546

Source: Where I'm Calling From: New and Selected Stories

Source: The 7 Habits of Highly Effective Teens: The Ultimate Teenage Success Guide

Alvaro De Rujula, quoted in "Large Hadron Collider - The Search For The Higgs" http://www.youtube.com/watch?v=_XbKZwXK-3c; this quote can be heard at approximately 3:55 to 4:15 in the video. It is important to note, it could be taken out of context. It implies that science is what we use when we do not know the answer to something.

Misattributed
Variant: We are what we repeatedly do, therefore excellence is not an act, but a habit.
Source: Will Durant, The Story of Philosophy: The Lives and Opinions of the World's Greatest Philosophers (1926), reprinted in Simon & Schuster/Pocket Books, 1991, ISBN 0-671-73916-6], Ch. II: Aristotle and Greek Science; part VII: Ethics and the Nature of Happiness: "Excellence is an art won by training and habituation: we do not act rightly because we have virtue or excellence, but we rather have these because we have acted rightly; 'these virtues are formed in man by his doing the actions'; we are what we repeatedly do. Excellence, then, is not an act but a habit: 'the good of man is a working of the soul in the way of excellence in a complete life... for as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy'" (p. 76). The quoted phrases within the quotation are from the Nicomachean Ethics, Book II, 4; Book I, 7. The misattribution is from taking Durant's summation of Aristotle's ideas as being the words of Aristotle himself.

Variant: We are what we repeatedly do. Greatness then, is not an act, but a habit
Source: The Story of Philosophy (1926), p. 87. The quoted phrases within the quotation are from the Nicomachean Ethics, Book II, 4; Book I, 7.
Context: Excellence is an art won by training and habituation: we do not act rightly because we have virtue or excellence, but we rather have these because we have acted rightly; 'these virtues are formed in man by his doing the actions'; we are what we repeatedly do. Excellence, then, is not an act but a habit: 'the good of man is a working of the soul in the way of excellence in a complete life... for as it is not one swallow or one fine day that makes a spring, so it is not one day or a short time that makes a man blessed and happy'.

Clary and Jace, pg. 137
Source: The Mortal Instruments, City of Ashes (2008)

The Value of Science (1955)