First let me introduce myself, my name is Leon and I've been training for almost four years now. Sounds like something from Alcoholics Anonymous but hey, we all have a story to tell, let me get straight to the point.
I'd like to talk about training solo. Most people find this boring to do, hard to find the self motivation, miss the social aspect of Parkour, maybe the team aspect of it, but unlike football and other team sports where everyone has their own role to play, in Parkour the onus is on you..
 Think about it, when you go for that kong to precision you cant opt out of doing the run up, pass on the kong to a mate (because you don't like kong vaults), or hand over the precision to 'him/her' because they are good at them, you have to go through the movements, the feelings, the emotions, the conflicts.... Alone!
Bear with me though you may disagree, group training is good and has it's benefits but, I guarantee with a different approach you will find solo training very rewarding.
I take the time to go out training alone and use a lot of these occasions to break jumps that have been haunting me for a long time. Jumps that I am afraid of, that seem too big, too far, too high, too technical. There's that something about them that shallows your breathing, increases your heart-rate, freezes your limbs, or makes your legs wobble, and your hands tremble, we've all been there.
My challenge to you is to go there and face some of your fears alone.
First let me clarify, we all know our own capabilities, our strengths, our weaknesses, our [current] limitations, be it physical, experience, ability or level of skill, so risks we are going to take are calculated on a personal level. The jump we are approaching is not one that is clearly out of reach, it is one that has been nagging you for months, maybe years. Through continued training and improvement there will come a point when you are ready, but one thing has not changed in that definitive moment when you are eyeing up that jump... The fear, it is still there....

Facing it alone.
This strips you bare, no false bravado, no spurring on, nobody there to 'do it first' to show you there and then the 'how to' and that it can be done. When training in groups you have sense of security, be it real or false, that you are in safe hands, there are people around to 'spot' you or to give you a helping hand (or call an ambulance) if something goes horribly wrong.
Now I don't mean to scare you and i'm definitely not going to share with you the thoughts that cross my mind when facing a challenge alone, but I'm sure you can piece together all the gruesome outcomes that wreck havoc in your mind. (waiver: none of the challenges I partake in include the potential outcome of death! I want to train for a long, long time. Rest peacefully in that knowledge friends and family)

Training solo and facing these challenges alone makes you stronger! You gain a fuller and better understanding of yourself, facing the mental riots makes you focus on your breathing, on relaxing yourself and slowing down that palpitating heart of yours. Increasing your self limitations and expanding that comfort zone.

I'm there all alone..
Time is ticking by...
I've played out the jump in my mind dozens of times... The approach.. The take off.. The flight.. The landing...
Time is ticking by...
I test out the surfaces...
Check my shoes..
Run up! Walk away! Breathe!
Time is ticking by...
I mock up a similar but safer scenario...
Drill it! Drill it! Drill it!
Time is ticking by...
I return to face my demon...
Breathe.. Approach.. Trust myself and my ability.. Launch! Fly!!
Time stands still for a split second..Land!!
I've done it! Hooray!!
The landing wasn't great, I didn't need that 100 metre run up. It took me an hour, or three, but hey that wasn't too bad! What was all the fuss about? I do it again and a few more times. Once is never! Perfect landing! Big Smile! Relief! Growth! Satisfaction."

Leon Lawrence.