Not even quite "won't tolerate having known bugs" - it's fundamentally acknowledging that you will at times find bugs in your code base - but that when you do discover bugs you'll prioritise fixing them above adding new features or hitting pre-set project deadlines.

It's a great philosophy or methodology, but it can be very hard to execute on 100%. In the real world there are deadlines and resource requirements and impatient clients and produce launch plans with set dates and trade shows starting next week and the Thanksgiving/Xmas launch opportunity and and and.