Why are Some Pieces so Long?

It used to bug me when I was a child that some pieces seemed to go on forever, especially the slow ones.

Thinking back on those feelings I see myself seated far back in an auditorium the size of Chicago's Orchestra Hall, supposed to be grateful to be there, but baffled as to what it was all about.

As a professional chamber musician I spent countless hours listening to performance tapes of complex works like piano trios, quartets and quintets--Dvorak comes first to mind in this regard.  His music perhaps more than that of any other composer is crafted to cause tonal instability to arise not because of structural reasons but strictly out of the auditory excitement of now this player, now that.

The good musician does not stop this excitement from affecting the course of the work, perhaps by throwing it momentarily out of tune, or causing some jagged entrances or other rhythmic upheaval.  All too often a well-meaning guest player would pull it all back in order, stressing the repeat aspects of a "theme" even though in entirely differently tonalities rather than relishing the variation aspects so skillfully composed into the work.

Trained to expect repetition where there is none we are not truly immersed in what is happening.  The music seems to never end.