Thank you for those links Don! I thought it sounded like Head and Heart - I should have checked myself. Hard to understand how that citation got mixed up.
I also noted a strange phrase in one of the quotes attributed to Epicurus - I will go back and look for that. It sounded like a variation I have never seen but it wasn't too far from the standard so I did not comment.
Godfrey I guess as to Jefferson I have a combination of reactions -- I cut him some slack for his usefulness and his perceptiveness in seeing Epicurus to be the superior of all Greek philosophers, but there are definitely some phrasings as you point out that tend toward asceticism. For example in the letter to William Short he combines the "don't be a slackard" comment (which is good) with some comments in his outline about "In-dolence is the absence of pain, the true felicity." That plays right into the hands of those who are giving the "abscence of pain" idea an absurd construction, and Jefferson should have realized that and been more articulate.
It's been a while since I read the "head and heart" letter but I do seem to remember that if you read the whole thing, and drill down to the conclusion, that Jefferson makes clear that pleasure / feeling trumps the dictates of "reason," so that is excellent. So that's the context if I recall correctly that that "retire within ourselves" comment may occur - but again I'd have to go back to the source. If indeed he meant "the art of life is the art of avoiding pain" as a stand-alone point that he emphasized as if it were clear on its on -- that definitely would be a huge problem for the way he is articulating the theory -- and certainly does not seem to be consistent with the way he lived his own life, so that would be very hypocritical.
Also Godfrey if you were to watch the video and listen to the narration, the writer goes significantly further in the wrong direction than the slides indicate. Maybe I will find the time to flesh out more of the transcript, but there are indeed statements made in the narration that are worse than the slides, and deserve to be pulled out and provided a response.
My comments here are rambling -- sorry -- but the ultimate point on Jefferson, Godfrey, would be that if Don is correct and that paragraph is an excerpt from the very long and detailed "head and heart" letter, then the probable response to the section that is quoted is that that is a part of the back and forth "debate" which is used a device in the letter, and by the time you get to the end of the letter it seems clear that Jefferson is rejecting excessive rationalism in favor of the position that the values of the heart - which presumably means pleasure - are what is really important in life.
If someone goes back and reviews the Head and Heart letter and disagrees with my characterization of it, please let me know. It's basically a love letter to a married woman (if I recall) so it's not written as an absolutely clear philosophical piece, and if I recall the very last part of it trails off into the ambiguity that arises from the context in which it is written. But I remember the effect it had on me was to very strongly state a winning case for "the heart" against the case for "the head."