A glowing, blue piece

A small piece,
But important, too.
It doesn't quite fit,
And it's an odd shade of blue...

It's like a purple box.
or a yellow tree.
Does this confuse you?
Many would agree...

Spinning in circles,
chasing imaginary foxes,
rocking in a chair,
or hiding in boxes.

Perhaps talking too loud,
Or drawing in silence.
It's a lasting enigma
with difficult credence.

"That shirt's too scratchy!"
But it doesn't feel rough...
"That music's too loud!"
But it's quiet enough...

Do you understand where I'm going?
Perhaps you live with it too.
Many people have it
So does it affect you?

A soft glowing light,
This piece doesn't quite fit...
But then, how many do,
In a puzzle you can't quit?