if there's one thing I love more than coding, it's using metaphors to explain to other people why they're not "getting it". like the all famous contractor:

"yeah I know you need 5 months to build my house, but can you do it in 2. Also, I'm going to pay half. Oh, and when the house is done, could you also add a cellar?"

any more good metaphors out there?

Pretty accurate.

When you have finished installing the central heating system, I'll tell you where I would like the radiators to be. I don't want to pay to move them if they are "wrong" though.

I enjoy pulling out the metaphor for adding another dev does not double efficiency; baking the cake at twice the temperature for half the time results in a burnt cake with a liquid centre?

Do you want burnt liquid code? No, so shut up, and be patient.

I love the "if I ask you to install a toilet, then I assume it is going to work" metaphor. Yeah, right.
I know plenty of plumbers... They make more than us!!!!! And if the price is not right, they will break you toilet on purpose.

Throwing 4 more devs on something only serves to piss off the one Dev who knows the project perfectly. And forces that one Dev to spend all his time fixing everyone else's sloppy code, because they feel that they own the project ... And rightfully so.