Quote from : The Spiritual Crisis of Man Book

(The presence of evil) in his life provokes him into either overcoming it or yielding to it. If the first, it has led him to work for his own improvement; if the second it has led him to acknowledge his own weakness. Sooner or later, the unpleasant consequences of such weakness will lead him to grapple with it, and develop his power of will...Immediately and directly, it may either strengthen him or weaken him. Ultimately, it can only strengthen him.