Why does the sun appear at the same zenith degree for three consecutive days during the summer solstice?

Why does the sun appear at the same zenith degree for three consecutive days (appear to stop moving for 3 days over the Tropic of Cancer) during the June Solstice; whereas, during the December Solstice the sun does not appear at the same zenith degrees but for one day (over the Tropic of Capricorn) and immediately begins its return journey towards the equator?