Ladders

The superstition of not walking under a ladder seems to be quite widespread – I always thought it was just common sense to stop someone dropping something on your head. But I recently found a reference that suggested it was because a ladder forms a natural triangle against a wall which represents the holy trinity and that stepping through this shows disrespect and will cause bad luck.

Any ideas seems a bit complicated to me, and does that mean it is only a superstition in Christian countries?