When it's almost midnight, and you're working on the most complicated lace you've ever made, when you have a chart you can barely understand and your progress is slow because you need to stare at the chart at all times, and you find a stitch several rows below that is actually in the right place, and there's no visible mistake (for a relative value of visible), but you split the stitch (knitting between the two strands of a 2-ply yarn)...
Trying to fix it before a good night of sleep is the worst idea ever.
I'm going to leave it until tomorrow, and then I'll try again. If I can't fix it, there goes 2 days of progress.