Our lack of confidence is not the result of difficulty; the difficulty comes from our lack of confidence.

Seneca argues that tasks which seem impossible prove easier in the doing, and that the hardship lies in our hesitation rather than in the task. The sentence is often quoted online as “It is not because things are difficult that we do not dare; it is because we do not dare that they are difficult”, which is another translator’s wording; this page gives Richard Gummere’s.