*flips a coin*
You know the probable outcome is 50/50, but how do you know this?
The first result will always be one way or another, there's no 50/50 result, and it's this initial result that creates a bias, a belief that one way is more likely than another, even after 100 coin flips with an outcome of 50/50 there's still that (irrational?) belief that because it fell one way the first time it's more likely to fall that way the next time, after all why else did it fall that way?
So you see there's a mechanism to human thought based upon observation and recognition of patterns within the observed data (real or not) and it's only on a more abstract level that we can figure out (rationally) that the probable result for a coin flip is 50/50, only 50/50, and will always be 50/50 unless some other factor is involved.
Unfortunately life is a lot more complicated than a coin flip, making it much harder to accurately calculate the probability of this or that happening, so we experience doubt which is basically our pattern-forming recognition system having difficulty figuring out what the right course of action is based upon observed patterns. The problem being that there simply isn't enough data, not enough to be sure anyway, and with insufficient data different parts of our brain which have received different data come to different conclusions and "argue", and it is this cognitive dissonance that we experience as doubt.
In our behaviour doubt manifests itself as inaction, simply because it's easier to fuck something up by doing the wrong thing than doing nothing (most of the time anyway) so responsibility falls upon the conscious/rational mind to make the call, like a king in his throne room surrounded by his advisors, it falls upon you to make the decision (in spite of there being insufficient data) utilizing whatever amount of wisdom you posses.
This “decision making” is essentially fooling yourself into believing you know what to do, there’s no escaping the truth of it, life makes a fool of us all, but are you a wise fool or just a fool?
You’ll see by the results of your actions.