For every why he had a wherefore.

-Butler, Samuel
  Hudibras, pt.1, canto1, l.132.

I'm called little Buttercupödear Little Buttercup, Though I could never tell why.

-Gilbert, Sir W(illiam) S(chwenck)
  HMS Pinafore, act1.

The person who knows'how' will always have a job. The person who knows 'why' will always be his boss.

-Ravitch, Diane Silvers
  Speech at Reed College commencement. Reported in Time,17 Jun.

   You see things, and you say,'Why?' But I dream things that never were; and I say 'Why not?'

-Shaw, George Bernard
The Serpent

Whence are we, and why are we? Of what scene The actors or spectators?

-Shelley, Percy Bysshe
Adonais, stanza 21.

Grand Dieu! Pourquoi suis-je moi? Great God! Why am I me?

-Stendhal pseudonym of  Henri Beyle
  Le Rouge et le noir, bk.2, ch.28.