Significant Passage

We are like you; the thought pressed into his mind. We did not mean to murder, and when we understood, we never came again. We thought we were the only thinking beings in the universe, until we met you, but never did we dream that thought could arise from the lonely animals who cannot dream each other's dreams. How were we to know? We could live with you in peace. Believe us, believe us, believe us. - Pg. 321

This quote come near the back of the book. Ender didn't destroy all the buggers as he thought. While playing the "game", the buggers read his mind to communicate with him. Just before they were destroyed, the buggers left behind a queen egg, so that when Ender found it, they could talk. Right now, the egg is telling Ender their reasons for attacking Earth in the first place. There are times when we mistake another person's intentions. We fight with them, and when we want to stop it, they want revenge. And so the cycle continues till one wears out.