I wasted $40k on a fantastic startup idea

I think that people are probably misleading themselves if they say they want it, but aren't willing to pay for it.

People fork over money for IAPs by the millions per minute, because they want the results.

I think if it were truly that desirable, people would have been happy to pay for it. I just don't think it provided that much value to the customer.

Mostly they're being polite (and showing they understand perfectly well how they could use it, so no need to explain its purpose any further thanks). They're not really misleading themselves...

Ultimately the author's problem is that he was showing Susan a clever project that looked much more attractive than notes she'd usually consult rather than asking her how many times a year she wasn't sure what to prescribe and how difficult it actually was for her to get a sound recommendation from a source she trusted.

Even if he was trying to demo a finished product rather than figuring out if it should exist, asking those questions would still have been more likely to put her in the frame of mind where she asks about or spots the really difficult to ascertain info that has professional liability repercussions rather than just liking the UI and being impressed that this programmer is citing the Hamilton Rating Scale for depression)