The reversible machine is like a car that coasts down a hill and up another to the same altitude without using any gas. It is a perpetual motion machine because there is no friction to stop it. It keeps the same amount of kinetic + potential energy forever. This does not violate conservation of energy, so it is not immediately obvious it is impossible. Feynman will show this is impossible because there is always some loss somewhere.

The machine lifts a weight > 3x is like a car that coasts to a height higher than its start. It gains energy from nothing, violating the conservation of energy law.

The reversible machine is like a car that coasts down a hill and up another to the same altitude without using any gas. It is a perpetual motion machine because there is no friction to stop it. It keeps the same amount of kinetic + potential energy forever. This does not violate conservation of energy, so it is not immediately obvious it is impossible. Feynman will show this is impossible because there is always some loss somewhere.

The machine lifts a weight > 3x is like a car that coasts to a height higher than its start. It gains energy from nothing, violating the conservation of energy law.

At this point, Feynman has shown that no self contained lift 3/lower 1weight raising/lowering machine can lift a weight higher than a revsible machine, and all such reversible machines lift 3 to the same height. But he hasn't shown what that height is. He now does so.