If I am not mistaken, Travis Pastrana came up with a formula for risk vs. Reward
It is based on 100 points. The Equation is the following:
fun +/ money, + reward,  risk.
Lets break that down
The move you want to do... How fun is it? Is it lame or is it pretty steezy? come up with a number.
Now
Are you being paid for it? no? Continue onto equation
Wahts the reward? Ego Boost? Bragging rights? + points based upon the reward of successful completion.
Now subtract the risk. How badly can you get fucked up by doing this trick? Are you going to scorpion with your face planting into the rail 20 feet in the air?
Once you have this number, its up to you decide, but this is what i think
if its above 80... no questions, do it.
If its above 60, think about it.
if its above 40... The risk is high, but still can be pulled off for self pride.
Below 15... The Risk doesnt meet the reward.
