Why do you always paint heads?

It is the topic of this 20x20 series.  On my larger paintings, I paint scenes, situations, plant-worlds, occasionally also technical equipment. Next to them, however, I enjoy painting these smaller pictures that have a lighter topic but which for me, however, are a painterly challenge that allows me to concentrate on a combination of multi-colours, which by equal light and colour quality stand in a defined relationship to each other which appear harmonic and nevertheless rich in contrast.  It pleases me to remain with one thing for a while.  Heads are generally appealing.  I travel 600 kilometers every week by train.  I have to wait a lot and sit among people thereby.  I observe the heads that are around me. Rather from their visual appearance than from the psychological side.  The reflection of the light and the colour phenomena that thereby emerge delight me.