Here is a great passage from this book, The Power Of Your Subconscious Mind by Joseph Murphy, that I have read:

Keep On Keeping On
When fear knocks at the door of your mind, or when worry, anxiety and doubt cross your mind, behold your vision, your goal. Think of the infinite power within your subconscious mind, which can generate your thinking and imagining. This will give you confidence, power, and courage. Keep on, persevere, until the day breaks, and the shadows flee away.

From past mistakes and failures learnt, we strive to overcome the same or new challenges tomorrow. As mentioned in the Joseph's book, in life we have to keep on keeping on.