Consider the original question. It's about someone jumping off a building, not someone flying off from a building.
We have all experienced gravity all our lives and it's a universal belief. It takes the kind of near impossible belief to overcome that. It's much easier to work with gravity in conjunction with other physical laws aka universal beliefs to fly with devices.
To jump off a building without devices is a test for or challenge to gravity, which of course already exists in the person's consciousness, whatever s/he declares.