"Contrast of Scale"
I don't think I really need to explain this one, but I will.
I LOVE music. I have about a zillion CDs and records. What's amazing to me is that instead of carting around a clunky personal CD player, or "Discman" as they were known in the olden days (for you kids out there who have no idea what I'm talking about) and a case full of CDs, I now have this handy dandy MP3 player that can fit hundreds of songs. This on a portable device that is only about the size of a credit card (and this puppy is over 5 years old! I shudder to think what the new fangled ones can do!).
These things are ubiquitous now. The ways that these devices have changed how we listen to and share music is profound - for better or for worse. The contrast of scale of my relic of a cd collection (that I still love and occasionally use, FYI) vs my MP3 player just about says it all.
See Monica's photo here.