“Masterpiece” suggests great art, but when the word first appeared in German as “meisterstuck”.
It referred to a medieval standard of excellence expected from an apprentice before being allowed to join a guild of master craftsmen.
After many years under the guidance of a master, the apprentice submitted a piece of work for assessment.
If his work or masterpiece passed the test, he would be allowed into the trade as a master craftsman.
And that’s why a crowning achievement is called a Masterpiece.