“Martinis are like breasts, one isn't enough, and three is too many.”

Variant of:
I wish I could drink like a lady.
“Two or three,” at the most.
But two, and I’m under the table—
And three, I'm under the host.
The Harlequin, Volume 2, 1959, University of Virginia (page ? http://books.google.com/books?id=zdFKAAAAYAAJ&q=%22under+the+table%22+%22under+the+host%22)
Perhaps attributed due to “One more drink and I'd have been under the host.” (see above).
“ Martini Madness: Dorothy Parker didn’t write the famous quatrain about martinis that’s always attributed to her. http://www.slate.com/articles/life/drink/features/2013/martini_madness_tournament/sweet_16/dorothy_parker_martini_poem_why_the_attribution_is_spurious.html”, Troy Patterson, Slate, April 8, 2013
Misattributed
Variant: One martini. Two at the most. Three I'm under the table, four I'm under the host!
Source: The Collected Dorothy Parker

Introductio ad prudentiam: Part II (1727), Gnomologia (1732)

"Touch of Evil: A selective investigation of recent mysteries and thrillers" http://www.theatlantic.com/magazine/archive/2006/04/touch-of-evil/304721/ (April 2006), The Atlantic
2000s

This seems to have originated with the Spanish military leader Juan Domingo de Monteverde, who, in Francisco de Miranda, a Transatlantic Life in the Age of Revolution (2003) by Karen Racine, p. 239, is quoted as having said: "four walls are three too many for a prison — you only need one for an execution."
Misattributed

Source: Obsidian Butterfly

Variant: There are too many books I haven't read, too many places I haven't seen, too many memories I haven't kept long enough

Les hommes construisent trop de murs et pas assez de ponts.
This became widely attributed to Isaac Newton after Dominique Pire ascribed it to "the words of Newton" in his Nobel Lecture, 11 December 1958. http://www.nobelprize.org/nobel_prizes/peace/laureates/1958/pire-lecture.html Pire refers not to Isaac, but to Joseph Fort Newton, who is widely reported to have said "People are lonely because they build walls instead of bridges." This appears to be paraphrased from a longer passage found in his essays and addresses, The One Great Church: Adventures of Faith (1948), pp. 51–52: "Why are so many people shy, lonely, shut up within themselves, unequal to their tasks, unable to be happy? Because they are inhabited by fear, like the man in the Parable of the Talents, erecting walls around themselves instead of building bridges into the lives of others; shutting out life."
Misattributed