It’s hard to believe many people really confuse the meaning of these words, but the spellings are frequently swapped, probably out of sheer carelessness. “Piece” has the word “pie” buried in it, which should remind you of the familiar phrase, “a piece of pie.” You can meditate to find peace of mind, or you can get angry and give someone a piece of your mind. Classical scholars will note that pax is the Latin word for peace, suggesting the need for an “A” in the latter word.
BUY THE BOOK!