Faith is a sure confidence of things which are hoped for and a certainty of things which are not seen

A succinct and crisp explanation of The Unavoidability of Faith by Miles Kimball.

Logic and data takes us only so far in our decision-making process, frequently not far enough. There are many circumstances where the necessity of a decision is unavoidable - you have to decide even though you are ill-equipped to do so and have too little pertinent data.

Kimball quotes Hebrews 11:1, William Tyndale’s translation with modern spelling.

Faith is a sure confidence of things which are hoped for and a certainty of things which are not seen.

Later,

One might be tempted to think of faith as a Bayesian prior. But it isn’t that simple. In Bayesian decision-making, “prior beliefs” are left unexplained. But in the real world they come from different ways of responding to and reasoning about past experience. New data sometimes simply updates prior beliefs within the same paradigm, as Bayesian theory suggests. But other times, new data upends the thin tissue of reasoning and reaction that was crucial for the formation of those prior beliefs, resulting in a much bigger change in views than straightforward Bayesian updating would imply. And sometimes additional reasoning—in the absence of any additional data whatsoever—can dramatically change one’s views.

A simpler point is that what is prior to one set of events is posterior to earlier events. Putting both points together, faith is what one believes at a given moment in time, however one has managed to cobble together those beliefs.

In situations where one is willing to think of one choice as inaction, with costly actions having debatable benefits, one can distinguish between a “belief in nothing” that leads one to continue in inaction, and a “belief in something” that leads one to act. When proponents of action say “Have faith!” they are advocating a belief in a high enough marginal product of action to make it worth the costs.

We all like to believe that our beliefs are founded on rock solid rationality and empirical data but usually we are running on a rich mix of assumption and opinion, garnished with some occasional facts.