The authority of the sages

Where does the authority of the sages come from?
I would love a rational answer.

And who am I allowed to disagree with? For example, am I allowed to disagree with the Malbim or with Rav Kook or Ramchal?
If not, why?
When I say I disagree, I mean my perspective on the subject, which I have researched in depth from all angles and which seems different to me than what that rabbi says.
Or do I think he looks at reality and rules this way and that because of the world he comes from (Haredi, liberal, national religious) and that influences his ruling.