Well yeah, the Lisa might have been a failed PRODUCT, but it wasn't a failed technology.
Whether the Mac is a parallel product or an evolved product, the point is that the idea of user friendly computer with a WYSIWYG, mouse based GUI was not a failure. This was an early unsuccessful attempt, but in the long run the problems and costs were sorted out.
You are working on a machine right now, no matter what the brand of OS, that took those basic ideas and made something successful out of them.
And the Newton... same thing. It's Version One of a new tech. The Newton failed, but the Palm arose out of it, and from there a whole world of handhelds and now smartphones.