Without much reflection, the single most important consideration in terms of improvement to mental agility appears to be: “supposing this is true, what then?”
Contrast “but that’s wrong” and “why”, neither of which basically ever actually help anything. The former only works when you’re in power and probably isn’t optimal even then. The latter is only useful after-the-fact and is overhyped thanks to IFLS types, if you’re at all generally educated on your subject matter your initial judgement is going to be ~90% on the mark anyways; “why” is a self-inspection tool to grind out that last ~10%.
The second most important would be “Yeah nah go fuck yourself”.