The Y and the I in Middle English

Scribes felt that an I at the end of a word was particularly hard to read, so it became an almost universal practice to avoid an I. That final I could be avoided by simply replacing it with a Y. But if the word had a suffix, the I could be retained because it was no longer sitting there at the end in Gothic script. So when we say that we drop the Y and add an I along with the suffix, that's actually the opposite of what happened. It was the I that was dropped in the simple form of the word and the Y was put in its place.