The difference between certainty and uncertainty

Certainty - firm conviction, with no doubts, that something is the case

Uncertainty - the conscious awareness of ignorance 

-from The Art of Uncertainty by David Spiegelhalter 

All investors deal with issues of certainty and uncertainty. Importantly, there is no certainty. Get that out of your head. We live in a world of probabilities from what is countable and a world of uncertainty based on ignorance. Uncertainty is foremost what we do not know, so the job of any analyst is to reduce uncertainty from ignorance. There is some uncertainty that we will not be able to fully learn our way out. In those cases, we have to make some subjective probabilistic judgments. 

All investment research is about reducing uncertainty and increase the precision of our probabilistic estimates.