Stairs (as well as windows/doors) are metaphors for the unknown. When viewed, the question of where they go, or what's behind them, naturally arise.
When I was in college, there was a girl studying art therapy. She had to "analyze" a body of work by another student, but one she didn't know personally. She chose me. I gave her a bunch of prints and proof sheets. I had a lot of doors and windows (a few stairs, too). It was from her that I learned of the metaphor. She concluded that my work showed an obsession with "death and sex" (2 unknowns). I told her, "I hope it's not in that order. I'm only 20".