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It suggests that if you want something to end well, you need to begin it well. Starting something in a half-hearted manner is unlikely to return a high quality result.
This phrase is often attributed to the 20th century American writer Louis L’Amour. The proverb was in fact 600 years old when L’Amour began using it. The first example of the proverb in print is in the collection of biographies known as The South?English Legendary, circa 1300.