Thank you for giving two examples (REST, and style conventions). I was hoping to get examples from you but didn't ask.
I think actually both examples you gave show that the opinion was not "weakly" held: for REST, you mention "if a team presents a reason... and makes a case". For style conventions, likewise, "we can change direction" but the whole point of a uniform style guide is that the style convention itself has huge momentum and can be changed only if there is a very specific case where it "fits better" (your words).
So it seems what we're really saying is something like "we know what we think, but we think about what we 'know'." (I tried to be pithy but came up a bit short.)
Is that a fair summary? That it's about both assertively knowing something, but also being ready to rethink it (if there is a case)?