Fear is difficult to overcome. You are constantly thinking about what could happen or what will happen, that it doesn't matter the width of a cliff ledge or school corridor; it will always be easier to walk a school corridor. Ask yourself this: Would I rather walk on the edge of a cliff, where I could fall, or along a school corridor, where I could bump into walls? The answer should be simple. A school corridor, no der. Now ask yourself why. I would say, "Well, bumping into a wall is a lot better than falling off a cliff!!"
Because of your fear that you <em>just might</em> fall off the cliff makes it a lot harder to walk along a cliff ledge than a school corridor, no matter the width.
Atticus then asks, "Then whose blanket is that?" Scout then becomes aware of the blanket across her shoulders. As Jem is remembering the events, he recalls that Mr. Radley was fighting the fire with the other men, which means he could not have been the one to cover Scout with the blanket.