I think that social pressure is one the biggest things to overcome when starting something like parkour or any 'extreme' sport. These sports are supposed to be for kids, etc, etc... My wife would be perfectly happy if I:
gave up snowboarding, climbing and mountain biking and...
...when in the playground with the kids sat on my arse chatting politely with all the other sedentary parents.
Sorry, but I enjoy playing too

Of course this backfires sometimes - my 2 yo gave me a lecture the other day telling me the benches are for sitting, not for jumping over
Seriously though, I haven't progressed with my parkour enough yet where high risk maneuvers are much of an issue, but I still feel hesitant about the possibility about of either faceplanting in front of my peer group (other parents) or having to explain the large bruise somewhere or other to my wife...
Until I've fully developed my do-not-care attitude I presently either find out of the way places to drill (trail-running, running at lunch - parks are wonderfully empty) or by taking my kids to the park and playing while they play.
There is hope for me yet though. During Saturday's town election, while my wife was responsibly advocating for her candidates, I was running around the school yard (which is where the polls were) with my daughter taking every opportunity I could find to vault, climb, roll and hang upside down from things. My wife was even too busy to give me dirty looks

Several years ago, I was snowboarding in Utah and took one afternoon to take a lesson. The class consisted of myself and a 70 year old guy who had been snowboarding a few years but really wanted to learn how to get big air (his words). He's been my role model ever since.
P.S. I did take time out to vote - I can be responsible too.