I judge success by what sounds good enough to make it onto (and stay on) one of my pedalboards....
^^^Using that as a yardstick, my success rate is maybe 0.01%
I get bored really easy and I enjoy the layout design and build process.
I enjoy the layout design process more than any other part of building pedals by at least 1000%
I REALLY REALLY enjoy designing boards.
These days my success rate of firing up first time depends on the circuit.
On something I have never built before...
(Success rates may be lower if I get any distractions during the build process)
If its a new layout of an existing circuit, probably about 80% - 85%.
If its an existing circuit and a verified layout, these days probably 90% - 95%
New circuit, new layout: about 75% - 80%. After verifying the circuit on a breadboard first.
I started working with electronics and on circuit boards and cables (building MASSIVE cable harnesses) since 1981.
When I first started building pedals (5 - 6 years ago?) my success rate was much lower, maybe 40% - 50%
I think I have a pretty good success rate.
But when working on a build I have never done before, I work very slowly and methodically.
Same with something I have built before, but distractions have a less drastic effect on me then.