The Sensible 12: No. 4

4. The project must deliver a quality product or service.
There is no sense in embarking on a project unless the quality of the product or service that results from that work meets or exceeds the expectations of the customer. Even if the project is delivered on time, within budget and with the defined scope, it will be a failure if the quality isn’t there. Quality should be considered from the beginning of the project and at the forefront of everyone’s mind throughout the project.

Quality is a fake forth factor in projects. The only 'quality' is that the technical performance is delivered when required to produce the return sought (they always go together). There is no separate 'quality' parameter!
If technical performance is not achieved, the project is not 'done'. "Quality" then becomes an irrelvant overlay.
For example, a door has to stay on its hinges and latch shut when closed. If it does not  do this, then it is not that it is a 'poor quality' door, but that it is not functioning as a door at all. There is no door if the lump of wood won't swing on hinges and latch closed.