“I give myself sometimes admirable advice, but I am incapable of taking it.”

Source: Ghost Story

Source: The Dangerous Summer (1985), Ch. 1

Variant: She generally gave herself very good advice, (though she very seldom followed it).
Source: Alice's Adventures in Wonderland & Through the Looking-Glass

Letter I : Abelard To Philintus, as translated by John Hughes<!-- 1782 edition -->
Letters of Abelard and Heloise
Context: Sometimes I grieve for the house of the Paraclete, and wish to see it again. Ah, Philintus! does not the love of Heloise still burn in my heart? I have not yet triumphed over that happy passion. In the midst of my retirement I sigh, I weep, I pine, I speak the dear name of Heloise, pleased to hear the sound, I complain of the severity of Heaven. But, oh! let us not deceive ourselves: I have not made a right use of grace. I am thoroughly wretched. I have not yet torn from my heart deep roots which vice has planted in it. For if my conversion was sincere, how could I take a pleasure to relate my past follies? Could I not more easily comfort myself in my afflictions? Could I not turn to my advantage those words of God himself, If they have persecuted me, they will also persecute you; if the world hate you, ye know that it hated me also? Come Philintus, let us make a strong effort, turn our misfortunes to our advantage, make them meritorious, or at least wipe out our offences; let us receive, without murmuring, what comes from the hand of God, and let us not oppose our will to his. Adieu. I give you advice, which could I myself follow, I should be happy.

"The Beatings Must Continue" http://krugman.blogs.nytimes.com/2013/04/30/the-beatings-must-continue-2/, 30 April 2013
The Conscience of a Liberal blog

Trial of Dewhurst and others (1820), 1 St. Tr. (N. S.) 607.

Un fat quelquefois ouvre un avis important.
Canto IV, l. 50
The Art of Poetry (1674)

Source: Notes of a Dirty Old Man

Source: The Haunted Mask II