Robert Frost: Trending quotes

As quoted in The Harper Book of Quotations (1993) edited by Robert I. Fitzhenry, p. 261
General sources
Variant: In three words I can sum up everything I've learned about life: it goes on.

St. 1
Source: Stopping by Woods on a Snowy Evening (1923)

Variant: A diplomat is a man who always remembers a woman's birthday but never remembers her age.

The portion of "The figure a poem makes. It begins in delight and ends in wisdom." is often misquoted as: Poetry begins in delight and ends in wisdom.
The Figure a Poem Makes (1939)
Context: It should be of the pleasure of a poem itself to tell how it can. The figure a poem makes. It begins in delight and ends in wisdom. The figure is the same as for love. No one can really hold that the ecstasy should be static and stand still in one place. It begins in delight, it inclines to the impulse, it assumes direction with the first line laid down, it runs a course of lucky events, and ends in a clarification of life-not necessarily a great clarification, such as sects and cults are founded on, but in a momentary stay against confusion. It has denouement. It has an outcome that though unforeseen was predestined from the first image of the original mood-and indeed from the very mood. It is but a trick poem and no poem at all if the best of it was thought of first and saved for the last. It finds its own name as it goes and discovers the best waiting for it in some final phrase at once wise and sad-the happy-sad blend of the drinking song.

" The Secret Sits http://www.poemhunter.com/poem/the-secret-sits/" (1942)
1940s

"Hyla Brook" (1920)
1920s

"Stopping by Woods on a Snowy Evening" (1923) http://www.poetryfoundation.org/poem/171621
Variant: And miles to go before I sleep.
Context: The woods are lovely, dark and deep.
But I have promises to keep,
And miles to go before I sleep,
And miles to go before I sleep.

Variant: Half the world is composed of people who have something to say and can't, and the other half who have nothing to say and keep on saying it.

Mountain Interval (1920), 5. In the Home Stretch, Line 187-192
General sources
Context: “My dear,
It’s who first thought the thought. You’re searching, Joe,
For things that don’t exist; I mean beginnings.
Ends and beginnings—there are no such things.
There are only middles.

" Fragmentary Blue http://www.ketzle.com/frost/fragblue.htm", st. 1 (1923)
1920s

Variant: You are educated when you have the ability to hear almost anything without losing your temper, or your self-confidence.

"The Death of the Hired Man" (1914)
1910s