Hmmm, I smell a general case...

Our best estimates put the number of x in the world at around y.

Applying the 80/20 rule you can estimate:

Of those, 20% (y(.2)) want to z

Of those, 20% (y(.2)(.2)) have enough motivation to start educating themselves about the process

Of those, 20% (y(.2)(.2)(.2)) will actually start building something

Of those, 20% (y(.2)(.2)(.2)(.2)) will actually finish building something

Of those, 20% (y(.2)(.2)(.2)(.2)(.2)) have prepared themselves enough to achieve some measure of success