"When the going gets tough, …"

[Arnold Zwicky]

"the tough get going". This proverb figures in a posting on a Zippy cartoon, here:
  http://arnoldzwicky.wordpress.com/2013/04/12/body-language-and-lithuanians/

in that posting, i quote Wikipedia speculations about the source.  i can't at the moment locate my copy of the Dictionary of Modern Proverbs, so i don't know if it's in there.  anyone have the skinny on the proverb?

arnold

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