Mood

I think power quality has a lot to do with it.  Sometimes my system sounds bad and Most of the times it is clean and crisp.  Maybe justification for a power purifier.  

Get some mood lubricant and keep it ready for next time. :)

Great topic you teed up. Some days my system sounds awesome and some days it  doesn't quite get there. As noted above, "ear lube" helps my system and "swing lube" helps my golf game.  I embrace lubricants for a variety of enhancements in my life.  At any rate, the vicissitudes in the sound of one's system, day to day, is a matter that resides between one's two ears, I think.

@whitestix 

 I embrace lubricants for a variety of enhancements in my life

Careful you don't slip and crash into a speaker or land face down on top of a hot tube amp! 

@noromance 

I don't want to hijack this thread so I will PM you. 

A trap that we fall into is thinking a bad sounding track is the fault of our system.

Accept the fact that there are bad sounding sources and that not all sources are created equal.