"I welcomed the fact that now we had a binding liturgical text after a period of experimentation that only deformed the liturgy. But I was dismayed by the prohibition of the old missal, since nothing of the sort had ever happened in the entire history of the liturgy. The impression was even given that what was happening was quite normal. The previous missal had been created by Pius V in 1570 in connection with the Council of Trent; and so it was quite normal that, after 400 years and a new council, a new pope would present us with a new missal. But the historical truth of the matter is different. Pius V had simply ordered a re-working of the Missale Romanum then being used, which is the normal thing as history develops over the course of centuries. Many of his successors had likewise reworked this missal again, but without ever setting one missal against another. It was a continual process of growth and purification in which continuity was never destroyed."
-Milestones: Memoirs 1927-1977, by J. Card. Ratzinger, pages 146-47