Einstein's Equation for Success

The equation for the equivalence of mass and energy, E=mc², was discovered by Albert Einstein, and is particularly popular. Do you know Einstein's equation for success in life? It is also quite simple and yet has a deep meaning.

If A is success in life, then A equals x plus y plus z. Work is x; y is play; and z is keeping your mouth shut. — Albert Einstein

Rewriting the above words in the form of an equation, we get:

A = x + y + z,

where A = success, x = work, y = play, and z = (mouth shut).

We know the following two proverbs: (1) All work and no play makes Jack a dull boy. (2) Speech is silver, silence is golden. Einstein succeeded in unifying these proverbs into a single equation, though his quest for a unified theory of everything was too much ahead of time and fruitless.

I have learned the above words of Einstein from Ref. 1, but do not find them at least in the original edition I have of Ref. 2.

Note added later: The source of Einstein's words given here is described in Ref. 3 as follows:

Said to Samuel J Woolf, Berlin, Summer 1929. Cited with additional notes in The Ultimate Quotable Einstein by Alice Calaprice and Freeman Dyson, Princeton UP (2010) p 230.

References

1. RSICC Newsletter, No. 486, Radiation Safety Information Computational Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, U.S.A. (August 2005).
2. A. Calaprice, ed., The New Quotable Einstein (Princeton University Press, Princeton, 2005; the original edition The Quotable Einstein published in 1996).
3. "Albert Einstein," Wikiquote, at the end of "1920s" (14 January 2012, at 18:41).