Just came up with another one!
This evening I was cutting out block 4 of a BOM using templates and got ready to sew only to discover that I was supposed to have cut a 2" strip and 4 triangles out of one fabric, but I had cut 8 triangles. I guess I was looking at the directions for another fabric. Now I don't have enough fabric to cut the 2" strip. Boo! Back to the LQS for another piece of fabric for one lousy 2" by 11" strip!