I feel like I should place the "Marketing" section higher. There's a list of questions to do a market research before even starting and discover if the fundamentals of your product are correct.
Most start-ups aren't solving any huge problems, and sometimes market inefficiencies are there for a reason (see all the start-ups involving the field of law, for example).
Even for the ones that are solving a big problem (that people are willing to pay for), it's very uncommon to have no competitors.
So typically the way to make a successful company is to be better than your competitors, and the way you do that is through customer support, UX, etc.
So to your credit, I think for most start-up founders this is the way to move forward. But it's definitely a bit of a sunk cost fallacy - it's really hard to admit your idea will never be successful and to start over from scratch.
It's easier, and has more obvious ways to measure success, to adjust relatively minor things.
