I went to get a new water filter for my several-months-old refrigerator yesterday, at Sears. I put the model number on a piece of paper in my wallet and went forth.
I need a filter, and have the model number here, I said. "Is it a Kenmore?," he asked. Yes, it is, I replied. "Is it a side-by-side?" Yup. "Is the filter in the grille on the bottom?," he asked, pointing at an example. Yes. "I don't need to look up the number, that's easy, this is the one you need." I paid and left.
It was the wrong filter.