To partly answer my own question - clearly there is work we can do that is net-positive. I can spend my time turning a crank to charge a battery, and sometime l

To partly answer my own question - clearly there is work we can do that is net-positive. I can spend my time turning a crank to charge a battery, and sometime later get back a subset of the energy I put in. Or, I can spend that amount of time digging up coal, or building a solar panel, and then sometime later have access to many multiples of the amount of energy that I put in.