I forgot to wind the yarn into a ball
It didn't occur to me until I was two rows in that maybe it might be easier if I didn't try to knit the scarf while the yarn was still wrapped up in it's skein. By then it was too late to save the the yarn - it had already wound itself into such a knot that I ended up frogging what I had done and then spent most of Friday night and Sunday undoing the God awful mess.
Everything is mostly untangled now (once the yarn ball reached a certain size, I snipped the yarn, so now I just have a small knot to deal with) and I re-casted on the scarf Sunday night. I'm 18 rows in and almost done with my first stripe. I just need to remember to wind the yarn before using it and all should be fine!
How is your Work In Progress going?