What an interesting conversation. I would like to add:

You never know completely, that is the point. You are asked as a human to make your choice without having the certainty of being right or wrong in fulness. There is no outer authority or objectivity which will support you in your decisions or speeches other than your situational relative knowledge and wisdom.

You could ask yourself of the probability of a thing and then head towards the direction or avoid it, depends on the situation and circumstance in every single event.