Certainty is a rare and precious experience – it means you are the custodian of a truth. It is not a belief, however, fervent. It is not an instinct, a hunch, an insight or an idea. It is an incontrovertible truth of which you have direct knowledge. It may be of little consequence or have the power to permanently change a person, a country or even the world. But it is yours to protect now if you have the strength to do it. You should resist the temptation to raise your voice. This is a sign of weakness which your opponents will exploit.
Resist the urge to speak quickly. If interrupted, pause and listen. The truth can wait. Allow your opponent to finish as you wait patiently, analysing their interruption for both strengths and weaknesses. Where their objection has merit, strengthen the expression of your truth, where their objection is weak, point it out with grace and humility.
Clarity is about making a few simple points clearly, not about making many points in a babbling attempt to assuage your own feelings of insecurity.