Shun not a riddle

quiet, simple, daily I come,
or at least one hopes.
for some, I am avoided,
set aside for other attractions.
others rejoice in my advent,
and embrace me as one would
a long lost friend.
some overindulge in me
and I, in bemusement stand by.
to others, I fear, I am like a flitting butterfly,
almost impossible to catch.
without me for too long and you may begin to show
the characteristics of inebriation.
other times, I sneak upon the unsuspecting
and wreck havoc in their existance.
without enough of me, you are sunk.
with too much of me,
you may miss out on the chance to earn daily bread.
I think your IQ may be affected if you shun me. how sad!
who am I?