Parkour belongs to the ones who live it, not the ones who want to live thanks to it. - David Belle

Down there we know, the streets we know, but up here? Nobody's been here.

Understand that this art has been created by few soldiers in Vietnam to escape or reach: and this is the spirit I'd like parkour to keep. You have to make the difference between what is useful and what is not in emergency situations. Then you'll know what is parkour and what is not. So if you do acrobatics things on the street with no other goal than showing off, please don't say it's parkour. Acrobatics existed long time ago before parkour.

If someone puts you in front of a 30m high wall, tells you to get over it, and then comes back two years later and you're still there, you've made no progress. You should find another wall.