Honestly, I still don't understand it (how the effect happens).
From a given location on Earth, at a given time of day, the sun does not appear at the same place in the sky each day.
Earth’s axis of rotation is tilted with respect to its orbital plane around the sun. Earth’s orbit is also slightly eccentric. These combine to form the figure-8 pattern of the sun’s position in the sky, or the pattern traced out by the shadow of the roof corner on the driveway.