Here is the keystone, and it's the one that makes the rest safe to write down. Every tenet before this is a position that is argued, opinionated, and therefore capable of being wrong for the problem in front of you. A rulebook can't admit that; a philosophy must. So the canon ends by handing you permission to break any of it.
The permission costs a reason, a real one, that names what this tenet would buy you here and why that price isn't worth paying this time. "I don't like it" is not a reason; it's the absence of one, the same defaulting the second tenet warns against, now wearing the costume of independent thought. "We've always done it the other way" isn't a reason either. "This boundary would cost us a day of indirection to guard against a change this prototype will never see", now that is a reason, and it makes ignoring a tenet the intentional move.
That's the whole distinction the site is built on. A reasoned exception is intentional code. An unreasoned one is just the default with better marketing. The tenets exist to make you say, every time you depart from one, what you traded and why, which is the only thing any of them were ever really about.