The Peacock and Juno explained simply

The Peacock was greatly discontented because he had not a beautiful voice like the nightingale, and he went and complained to Juno about it. "The nightingale's song," said he, "is the envy of all the birds; but whenever I utter a sound I become a laughing-stock." The goddess tried to console him by saying, "You have not, it is true, the power of song, but then you far excel all the rest in beauty: your neck flashes like the emerald and your splendid tail is a marvel of gorgeous colour." But the Peacock was not appeased. "What is the use," said he, "of being beautiful, with a voice like mine?" Then Juno replied, with a shade of sternness in her tones, "Fate has allotted to all their destined gifts: to yourself beauty, to the eagle strength, to the nightingale song, and so on to all the rest in their degree; but you alone are dissatisfied with your portion. Make, then, no more complaints. For, if your present wish were granted, you would quickly find cause for fresh discontent."