This is true in relationships and also pertains to moving, having to say goodbye to family and friends, making a career change, saying goodbye to old habits/lifestyles,etc. Be Brave enough to say goodbye and life will reward you with a new hello :)
The book was dedicated to C.S Lewis' niece, I think, Lucy. The dedication said something like this "I started this book when you were young enough to read fairy tales, but someday you will be old enough to start reading fairy tales again.
"And once the storm is over you won't remember how you made it through. You won't even be sure, in fact, whether the storm is really over. But one thing is certain. When you come out of the storm, you won't be the same person who walked in.