And the best bit: non-technical co-founders usually seem to believe that they should end up with 98% or so of the equity, because after all, you're a mere technician.
They continue going on meeting after meeting, looking for a mark. Meanwhile, the genuinely good non-technical (or technical, for that matter) co-founders are quickly selected out of the pool.
It's the same reason that you're far more likely to encounter someone who can't FizzBuzz during interviews than you are as a coworker: The developers who can't do the job are doing 10-50X more interviews than the developers who are good at their job, so you're going to see far more unemployable devs than employable devs with a random sampling of interviews even though most devs are employable.
Like 40% down to 2%
If you are looking to be a cofounder, "founding engineer" is far from it.
To be an equal you need equal equity but it is not that simple. Two friends holding 66% can dilute you, move your work into another company assgin a low value and cut you out. The many ways to get screwed is extremely high.