Nopony really knows how Derpy got her cutie mark or why she had a crossed eye. Nopony except Doctor Whooves and Romana. How did they know? They were there at the time. The time Derpy was brought to Equestria. The time she got her cutie mark. Time got them to know Derpy, but it also got them to leave Derpy.

And now, time was about to do something else.