Well this very question followed me through graduate school.
My first design assignment during my foundation year (2001) brought the issue of storing toothbrushes to light. My early solution focused on protecting toothbrushes from contamination.
But, it was two years later that I returned to the opportunity to refine my solution to also address the changing needs of consumers by focusing on the varying shapes of brushes as well as the increasing variety of interior configurations.
(see prototypes below)