One of the major themes of the book is defining "quality" and "value".
Perhaps a bit with Chris, though, and maybe that is what you meant.
Back to the 'whole selling point' I think he was being overly dramatic, it's a novel after all. I think his point comes across better when he goes through the value traps part of the book, and interpret his point the following way:
Sometimes you are working on some machine (physical, like his motorcycle, or abstract, like software), and you get stuck on a problem due to a seemingly very meaningless part of said machine. I think his 'whole selling point' message is: when this happens, you need to reassess the value you give this part, as, until you get to resolve what it is causing it to get you stuck, its value to you is pretty much the value of the whole machine. Like how a crashing bug means that specific software is useless, in the specific use case that triggers the bug, until that is fixed. If it's some weird edge case, the software may be perfectly usable for most people, but if you are one of the few affected by it, the most likely few lines of code causing the defect render the whole thing useless, they're the selling point of the software to you individually.
Now, obviously, speaking of the actual physical motorcycle, it's not that he can't sell it without resolving the problem that particular screw is causing him. There are probably skilled mechanics with the right training and tools for which the screw would cause little to no problem. But to him: he can't ride it until that is resolved, so the screw is as important as the entire machine until he gets that resolved.
I faced this specific problem just a couple of days ago and remembering the book (which I read years ago) helped me step away from the problem and come back to it with a fresh angle. But the reality was the same: it's not that I would have lost my physical entity (a window, in this case). Surely, I could have called a professional carpenter to help me with it. But to me, without getting someone else involved, that little piece (it was also a screw, a rusty one) was worth the whole window.