Enjoyed reading it, and also your writing style in general. Am saving the article in order to refer to when I start developing my new product idea. I have a genuine question, and maybe two further "optional" comments to offer since you're explicitly soliciting feedback.

The question: is there a distinction to be made between "startup" and "product"? How, if at all, would you change your process for a simple product idea, like, say, a new kind of umbrella?

As for the optional comments, I did find the "Read a book" a bit jarring in the bulleted steps of the process -- it is unlike the other steps in that you don't do it again and again for every single startup idea you might be evaluating, and so not really part of a process associated with each project.