When it looks totally fine, but you are looking at the chart, and it just isn't making sense; what this means is: Put down the lace and walk away.
Don't tink. Not yet.
Have a cup of tea. Perhaps decide that you are, in fact, reallllllly tired, and that it would be best to try again tomorrow.
You'll be amazed to find that when you look at everything again, your problem wasn't knitting the lace, but that charts look strange through crossed eyes.
I know this. Happened to me tonight.
Tomorrow is another day, right?
PS: I'm photo-journaling my knitting on flickr. So if you want to spoil anything for yourself (or not), then I warn you/invite you to find images there. I won't make a photographer, but you'll get the general idea.