"My concept is that there is more obstacles to cross than what we think.
For instance, I always recall that distance is the first obstacle of all. A "flat" one, though running up and down hills is not quite "flat". If you have to run for 2 hours, or even more, or 50 kms or more, you should be able to do it.
In many emergency cases, distance will be the most prioritary or difficult obstacle to clear. Long distance running skill is important, definitely.
Water is one of them, a liquid obstacle. What indeed if there's water across you way ? What if you must swim underwater a 50 m long distance ? Isn't that an obstacle that require only your human abilities to go from A to B sh*t ? Think of A to B when it's time to save your own life...
What if you simply fall into the water ? SWIM.
Same with air. Air, lack of oxygen, toxic smokes in a corridor or tunnel to cross can be an obstacle. If you must run that 100 m long tunnel without breathing or you'll die, better is to be trained for it.
Same with shoes. What if you were to loose your shoes ? Can you still run ? What if the ground is frozen, or very hot ? Or full of sharp stones ?
If parkour to you is only reproducing specific moves you've seen on vids, you're totally missing the point, because you're just limiting your practice to what you think it is. But parkour is not only the moves you can put a name on, guys wake up !
You must make sure what you train for is going to potentially save your life or other's when needed, so train your body and mind for it, and don't limit that training to what you only know. It is all about adaptation to about any situation. You must think of circumstances that were not expected.
Again, if you loose sight of this purpose when you train, you're only having fun. What pushed David beyond his own limits when he was a teen was that he was always imagining such demanding situations. He was creating them in his head, then had to find solutions to escape the fictive danger he had imagined. I know because he told me.
His dad was a first a soldier, then became a great firefighter, rescuer, lifesaver. He was trained by the Methode naturelle, and trained and inspired his own son using the same method, which motto is "Etre fort pour etre utile", to be strong to be useful.
Strong means complete, able to run, jump, climb, lift heavy objects, swim, fight (self-defense), to be fast, agile, endurant, brave etc...both physically and mentally strong. Useful is about helping others.
Parkour is simply a modern and mainly urban declination of this discipline and philosophy.
Don't limit your practice to only its visual aspect, and don't limit your philosophy to what only suits you.
It's not about fun, parkour is so much more than that.
If you don't get it, you're lightyears away from understanding its true essence." ~ Hebertiste

"Good swimmers don't make compulsorily good runners or jumpers and swimming doesn't make you more agile or endurant to parkour kind of efforts and moves.
Physical conditionning due to swimming is very specific, it has nothing to do with isometric kind of effort for instance. Take any swimmer than never trains parkour, apart from the technical aspect that obviously takes a while to master for a beginner, but regarding the only physical aspect, that swimmer will have his muscles all strained the day after. All simply because it's a totally different range of moves and efforts. So I don't think swimming is a great way to train the body for parkour. Swimming is a great way to train for...swimming, and obviously brings many physical benefits. Now, if you take a swimmer and a guy that never trains anything and ask them to try some parkour moves, the swimmer's better overall physical condition will be obviously an asset compare to the guy that never does any sport, for sure."

"Another illustration is running for instance. Obviously, training for a sprint is way different than marathon training, but there is more : running on a flat smooth distance and running exactly the same distance on a track and field kind of distance (up and down hill, with rocks, holes and bumps) is also a totally different kind of effort then adaptation (in the second case, you've got to be used to absorb more shocks, it's more a kind of isometrics effort, with many pace changes, plus better proprioception skill needed, so same distance, totally different kind of runner...).
Swimming is exactly the same. And this is why it's "easy" to be not too bad or even really good when you specialize a lot in any kind of sport or even specialty within a sport, but way more difficult when training to become a real complete athlete..."

~ Hebertiste