The only finite resource we have is our time, this should be the real currency of the world.
Discussion
You need to convert your time and your energy in something, in order to have it back later.
https://primal.net/e/note1d0hv76fq8w7hzl2m3c3t52xllrjhf9jptrv90ymmlygjxg63xawqwk3l0h
https://primal.net/e/note19xv2fcy4222m7sdafxry555g6u55cv7t9jt7yuek0mqsj5ewrnls79wtqf