Moody again?

Maybe I am just done with all the holiday hoopla, or maybe I am ready to get the old schedule back (you know, hubby at work and kids in school), but for whatever reason I am moody today!  I know God tells us that with Him we can be joy-filled and since we have free-will it is our decision to embrace it or leave it.  So, if we know that we have that available to us… that we can literally choose our attitude… why do we chose to be moody and snarky?  It is selfishness?  Pride?  Disobedience?  All of the above?