Because hardcopy just doesn't lend itself to efficient retrieval. Fortunately, digital images are different. With powerful, flexible, affordable and readily available computer-based tools and a little planning, drilling down on any specific image becomes a snap. And reorganizations that would take hours in hardcopy take seconds on your hard drive. The rest of this article describes the digital retrieval system I've worked out for myself, not as a recommendation but as an illustration of the issues and some possible solutions.
Many valid approaches are possible.
She then went on to tell of a 3-foot stack of papers and file folders on the desk of a client who could put his hands on any document in the stack in under 10 seconds. It was an ugly, inelegant storage system, but somehow, it was an effective retrieval system for him, and that was good enough for her. They left the stack alone. The retrieval system that works for you may differ substantially from mine. The important thing is to figure out what does work for you and then put it in place before you find yourself swimming in digital pictures.