One way I can put it is that a non-technical co-founder must bring tangible business skills, that's what they provide, not "the idea".

If a technical founder is sitting down and writing code until 2am on the weekends the non-technical founder better be making phone calls and sending emails, etc...

The inexperienced "idea guy" thinks by sharing "the idea" they have done their part and are just now going to sit and watch as the "the programmer" implements it.