Are you trying to unravel and

Are you trying to unravel and rip back your scarf?  Or did you tangle up the yarn that you already ripped back?Generally speaking, if you begin ripping back from the last stitch worked, your yarn should just pull off with a gentle tug or two.  I say "generally" because there are some yarns that are more difficult to unravel because they like to stitch together or wrap around itself -- yarns like Mohair, eyelash, railroad yarns.  And if the knitter has inadvertently split the yarn while working, this can make unraveling more difficult.If you are trying to rip back from the cast-on end, that is the beginning of your knitting, you actually need to pull the yarn through stitch by stitch since prior stitches are locked into place by subsequent stitches.