The value and rank of every art is in proportion to the mental labor
employed in it, or the mental pleasure in producing it.
-- Joshua Reynolds
Related:
Excellence is never granted to man, but as the reward of labor. It
argues, indeed, no small strength of mind to persevere in the habits
of industry, without the pleasure of perceiving those advantages
which, like the hands of a clock, whilst they make hourly approaches
to their point, yet proceed so slowly as to escape observation....