I wouldn't have anything to apply physical fitness to. I would also veer away from challenging things, and perhaps take the easier route. I wouldn't have had so many adventures in the outdoor world, and would have spent too much time sitting in front of my computer, the TV, or a games console, wasting life.
Parkour has not only bought me the physical discipline, but also the reasoning to never give up, and always do something enjoyable and challenging. I self taught my drums for three years, which was incredibly hard, all because of this new mindset I have. I'm trying harder than ever in school now, because of this new mindset.
Parkour also teaches me that there is always something more to achieve, something new to learn and discover. Whereas before I would do what I thought satisfactory and stop, now I keep going on for as long as I want to, knowing that I will always see improvement if I put the effort in.
In other words; life without parkour would suck.