[icebraining]

If you want to jump over a building, you need to depart the ground at the same speed as you'll hit it on the way down

Well, the horizontal speed can be gained more slowly (running before the jump). Only the vertical speed needs immediate acceleration.

[ericd]

Yeah, it's just that the vertical is much more than enough to kill you (more than the energy from jumping off the top of the building), so the horizontal is kind of irrelevant.