Because sometimes you need something, and you need it RIGHT NOW!
We were on the train, Amtrak to be exact, to West Virginia. It was 6 am, and the sun was up, and I had been awake since 2. I was tired, grumpy, and only wanted to sleep. Unfortunately, the light was making it tough. Luckily, I had my size 9 needles and a skein of black Riverstone wool worsted in my knitting bag. I quickly whipped up a pattern in my head: cast on 18 stitches, knit 3 rows, purl 1, (to make a lifted rib to keep it from being heavy on my eyes) for 20 rows, then decrease at the bottom edge for 4 rows, then increase at the bottom edge for 4 rows, then repeat the purl 1 row, knit 3 rows back for 20 rows. Bind off. I wove in the ties (using the remnant of the long tail cast on for one tie).
The increasing and decreasing made the notch for my nose. It really worked suprizingly well, and by 7:30 or so, I had a functioning sleep mask.
The other passengers must have been SOOOOOO jealous.