Someone said to Voltaire, "Life is hard." Voltaire replied, "Compared
to what?"  (In "The State of Humanity" by Julian L. Simon)

.. someone once said to Voltaire, `Life is hard.' To which he replied:
'Compared with what?'  (In  "Statecraft: Strategies for a Changing
World Statecraft: Strategies for a Changing World" by Margaret
Thatcher)

Many, many references to this (alleged) quotation appear on the Web. 
This could be apocryphal.  Please cite evidence that it is not and
that it can properly be attributed to Voltaire, such as a reference to
a work by Voltaire
or a work contemporary with Voltaire's life.