I'm studying Feynman's Lectures on Physics, and I'm not really understanding his reasoning here:
Consider weight-lifting machines $\overline{}$ machines which have the property that they lift one weight by lowering another. Let us also make a hypothesis: that there is no such thing as perpetual motion with these weight-lifting machines ... If, when we have lifted and lowered a lot of weights and restores the machine to the original condition, we find that the net result is to have lifted a weight, then we have a perpetual motion machine because we can use that lifted weight to run something else.
Now, I simply can't understand this. If we lift and lower $n$ weights with this machine, obviously the result is that $n$ weights have been lifted and $n$ weights have been lowered. I think then: "well, so everything that was lifted was lowered", but we can start the process with one weight already lifted.
Then when we return it to the original state, there'll be a lifted weight in total. I don't know how to reason with this, I think I'm not really getting the point there about perpetual motion. Can someone give some help on how to understand this properly and develop some intuition?