It started out small. When my son was maybe two or three years old he got his hands on a marker and doodled on his bedroom wall. His dad is an artist, and we're both a little bohemian, so we let the doodle stay. Soon my son drew another doodle, and another, and another. Over the next several years he covered his walls with drawings. He drew rocket ships and space aliens and things I couldn't identify.
Just before his 10th birthday these drawings were painted over. Now my son's walls are simply white (with a blue ceiling above). All I have left are the photographs.
Sometimes you think, "why not?" When we thought through the consequences of letting our son draw on the walls, all we could really think of was that we'd have to paint over them someday. Well ... no big deal. We'd have to repaint those walls eventually anyhow.