Intending to do something implies the belief that you can do it.
The direction of causality is the reverse, though, and the two are causally separated by the decision. One assesses a situation and arrives at a decision about what to do. The decision made, one acts to carry it out. The decision screens off the beliefs from the action: the action should depend only on the decision, not additionally on the belief. Thinking all the while “but what if I fail? but what if I fail?” is a useless distraction. When one realises this, one does not allow oneself to be distracted.
A concrete example, again drawn from specific experiences. If I decide to run to catch a train that I might miss, I do not put a mere 50% effort into it if I am only 50% sure of catching the train. On the contrary, the decision made, I will run as fast as I can, up to the point where the outcome has been placed beyond any reasonable doubt. Either I get on the train before it leaves, or the train leaves before I can get on. At that point I can stop running.
The direction of causality is the reverse, though, and the two are causally separated by the decision. One assesses a situation and arrives at a decision about what to do. The decision made, one acts to carry it out. The decision screens off the beliefs from the action: the action should depend only on the decision, not additionally on the belief. Thinking all the while “but what if I fail? but what if I fail?” is a useless distraction. When one realises this, one does not allow oneself to be distracted.
A concrete example, again drawn from specific experiences. If I decide to run to catch a train that I might miss, I do not put a mere 50% effort into it if I am only 50% sure of catching the train. On the contrary, the decision made, I will run as fast as I can, up to the point where the outcome has been placed beyond any reasonable doubt. Either I get on the train before it leaves, or the train leaves before I can get on. At that point I can stop running.