But you can not just take any words and say it is a metaphor. I can not say "this is a walnut desk" when it isn't and just claim that it's a figure of speech me

But you can not just take any words and say it is a metaphor. I can not say "this is a walnut desk" when it isn't and just claim that it's a figure of speech metaphoring a very solid and beautiful desk. A metaphor must be widely understood as such before you can use it.