The way we misuse phrases and quotations may tell us something about how our brains work. I give three common examples. The first is "Now is the winter of our discontent", which comes from Shakespeare's play Richard III. The line refers to an ebb in discontent (for the house of York in Richard III's case). Winter is meant to be a modifier of discontent. However, people almost universally use discontent as a modifier of winter as in there is an entire season of discontent and now we're in the winter part of it. Even Steinbeck used it as the title of his book to indicate a state of disaffection. Some rephrase it to "Winter of Discontent" which could be thought of as a clever ironic pun of Shakespeare. However, if you think about it "Winter of our discontent" makes most sense when used as Shakespeare did.
Now why is it misused? I think part of it is laziness. Most people have never read Richard III. However, it may also be evidence that our memory for language is an attractor (Hopfield) neural network. In this idea, memories are attractors in a dynamical system each with a basin of attraction. "Winter of our discontent" is remembered as a complete phrase separate from its component words. If it was incorrectly associated with disenchantment the first time we encountered it, then it may be frozen as such. So the next time we wanted to express the sentiment (and who is more poetic and profound than Shakespeare) we would call up this quote without an examination of the true meaning.
The second misquote is "If music be the food of love, play on" from Shakespeare's Twelfth Night. Most people use this quote as a positive statement about music. However, it actually is a negative statement about love. In the play, Orsino is heartbroken and wants to hear so much music that he will be come nauseated and no longer have any interest in love. In this case, I can see why it would be misused the way it has. Music is a surrogate for love so let's have more of it.
The third oft misused phrase and one that irks me the most is "begging the question". This term, which refers to a circular argument that presumes the truth of an assumption, is commonly used as a substitute for "raises the question". I've heard many hyper-educated people misuse this phrase. People will say "The fact that X happens begs the question...". I think in this case, people have heard this term in their youth but never understood what it really meant. However, it remained lodged in their memory and is now retrieved whenever a situation calls upon a particular question. In time I think this new and incorrect usage will eventually dominate and become accepted. This is too bad because now more than ever we really need to challenge those that "beg the question".