Yeah, and then get fired for not being productive.

No, how does that go? Esp. in jobs where there's no paint involved eg, fast-food service....

It’s a metaphor. Since most people are paid by the hour, it means you need to pace your work to fill up the time allowed to do it.

But it sounds like there's always plenty of work to be done at OP's place of business (Why else would OP's boss be worried about being shown up?) else they'd hire temps to augment the staffing as need be. People who don't do their jobs fast enough tend to get fired ... and hopefully too this particular boss asap ... unless they already have tenure. Sound like anybody you know? ;-) And if I'm paying some guy to either paint one room or my entire house, it ain't by-the-hour, but for the task itself. He can find his own damn motivation on his own time. ;-)

Oh please, there are assholes that make a job harder because say the job takes an average of 15 minutes per task, Mr. over achiever swoops in and does it in 5, now EVERYONE who in all honestly may not be able to do it in 5, is still expected to do it in 5. Slow the fuck down and chill the fuck out OP, your boss just gave you permission.

Being the go-to person & ultimately making the boss look good only works though if said boss is self-assured and intelligent enough to recognize that. In OP's situ, that doesn't seem to be the case. :-(