Use Only One Metaphor

I remember my first editor telling me I needed to stick to one metaphor. I didn't understand what he meant. What's wrong with two?  But now I get it. 

For illustration of this "less is more" concept delivered ever so deftly, see Bucky Fuller's "Operating Manual for Spaceship Earth:"

One simple image has so so much "go" 

 Can't get that floating piano top out of my head

Can't get that floating piano top out of my head