THE LITTLE THINGS
I once read that good design goes unnoticed (because it's intuitive/useful), but bad design never does (because it inconveniences the end-user). Applicable to any field, but especially apparent in product design, I was reminded of this after grabbing a cart from a new Price Chopper.
Gone are the days of big, rusty, cumbersome carts, to light, plastic, compact ones with added areas for drinks/small objects for shopper's convenience. Never underestimate the importance of your audience and the power/impact of smart design!