There's something special about a cyclist's shadow when the sun has just come up or is just going down.
It's the same reason many cyclists will watch their reflection when riding by a reflective glass building.
It's because we see other cyclists all the time. Stare at the wheel in front of us for hours on end, notice the cadence, the position, the hold on the handlebars. And it's the normal human thing to do to wonder: what do I look like on my bike?
But the shadow is something different. You could see your movements, but it's an exaggeration - when going up an incline it makes you looks as thin as the thinnest TDF climbe. It's not you, but it's you.
I haven't quite put my finger on it, but there's something to it. Something a bit mesmerizing.