So how do we assess the risk?
Mostly we fall back on experience. When we decide to pull out into a line of traffic we are using the numerous times we have done it before to imagine the outcome. We judge the speed of the approaching vehicle, we check for other dangers and we know the speed at which we can accelerate, then we weigh it all up.
What about the same circumstance, but in a car you have never driven before? Do you adjust your assessment? Yes, you realise that your knowledge of the car is limited and you make an adjustment for it.
But what do you do when you don't have any relevant experience to fall back on?
We start with training and apply any similar experience we do have. Then later we apply good training disciplines and once we have good discipline we then increasingly trust and apply our relevant experience.
Unfortunately, as we have already seen, we are quite bad at assessing our own performance when we are fatigued or stressed. Worse than this, we tend to overestimate our ability to perform.