There are ghosts in our stereo systems. Phantoms of sound that do not physically exist in the real world.
We call them the center channel.
Think of how much time and effort we put into getting this phantom center channel to sound real.
For most people, the center channel is number one in importance. We typically get it to pop and sound real, then work on the rest of the soundstage until the center begins to degrade and that's where we stop and call it good.
You can easily tell if you've gotten the center channel right. Play a mono recording and if things are properly set up, the music from that monaural recording should be disconnected from the speakers and form a believable image.
And the good news?
Unlike home theater folk with their hardware center channels, ours are but an illusion we never need upgrade.