The Great Vawel Shift

People have a tendency to adjust their vowel sounds to keep words distinct. It produces a chain reaction, sort of like falling dominoes. A change in one vowel sound produces a series of related changes as the neighboring vowel sounds adjust. This type of chan shift usually affects a small group of closely related vowels. But for some reason, this type of change shift affected all of the long vowels in english from the 14 hundreds through the 16 hundreds and it's never completely stopped.