Nothing in excess.

-Anonymous
Famous motto in  Antiquity.  According to Plato, the text was a temple inscription in Delphi (Hipparchus, 228e).

Virtue, then, is a state of character concerned with choice, lying ina mean†it is a mean between twovices, that which depends on excess and that which depends on defect.

-Aristotle
Nicomachean Ethics, bk.2, ch.6,1006 (translated by Sir David Ross).

L'amoureux qui n'oublie pas quelquefois meurt par exce'  s, fatigue et tension de me¤  moire (tel Werther). The lover who does not forget sometimes dies from excess, fatigue, and the strain of memory (like Werther).

-Barthes, Roland
  Fragments d'un discours amoureux.

The road of excess leads to the palace of wisdom.

-Blake,William
  The Marriage of Heaven and Hell,'Proverbs of Hell'.

Though taste, though genius bless To some divine excess, Faints the cold work till thou inspire the whole; What each, what all supply May court, may charm our eye, Thou, only thou can'st raise the meeting soul!

-Collins,William
  Odes on Several Descriptive and  Allegoric Subjects,'Ode to Simplicity', no.8.

Il ne faut se permettre d'exce'  s qu'avec les gens qu'on veut quitter biento"  t. We should never permit ourselves to behave in excess except with those whom we will leave soon.

-Laclos, Pierre-Ambroise Choderlos de
  Les Liaisons dangereuses, letter10.