EUCLID'S ELEMENTS, BOOK II, PROPOSITION 1

At certain times and conditions, things somehow become clear to me, that were previously unclear to me, under other times and conditions. For example, I read Euclid's Book II, Proposition 1, on October 10, and November 10, without understanding, while sitting in a different location, under different lighting. Yet, today, it is perfectly clear. I had misread the problem and became imprisoned by my imagination. Here is the proposition, see can you understand it. http://aleph0.clarku.edu/~djoyce/java/elements/bookII/propII1.html