The book is Tony Dungy's "Uncommon" which was given to me at Father's Day. Dungy begins Chapter 10 with a quote from William Shakespeare's Hamlet.
Now, I readily admit that, when it comes to Shakespeare, I am an ignoramus. I recognize some quotes that I hear from time to time, but not because I am actually familiar with the work. I recognize them because many have become part of the cultural fabric. Cultural Fabric, incidentally, can be purchased by the yard and is much cheaper in places like Miami, San Francisco, Las Vegas, Atlantic City and Austin, TX.
(Yes, the guy who knows nothing of Shakespeare IS making jokes about others lacking culture. But just ask yourself, where else are you going to find this kind of breath-taking irony at such low prices?)
The quote is this:
This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.
When I read this, I was flabbergasted. A little bit, anyway. Here, as I already mentioned, is a quote that I've heard before. That is, I've heard the "to thine own self be true" part. Usually on a TV show or in a movie is where I hear it and is usually deployed to justify some self-centered act. In other words, "you won't be happy unless you look out for Number One." But what I saw here, for the first time, was that the familiar part was nestled in a larger thought, roughly, be honest with yourself and you will be honest with others. At least that's how I understand it.
It is such a stark difference in meaning! "To thine own self be true", standing alone is an end in itself; "to thy own self be true" as a part of the larger quote is a means to an end. The former has self as its focus and latter has others as the focus.
The two meanings could not be more different.
Note: I have confessed my ignorance about Shakespeare and so I may have misunderstood him here. I'm willing to be corrected, if I have missed it. Let me know in Comments.