Yeah, what they said up there. I sometimes will catch the leg of a stitch in the row below too. I'm not sure which method I used for an inadvertent increase the other day but it was a few stitches from the end of the needle and I couldn't find it for the longest time. I was so ready to get rid of it I didn't take time to try to figure out what I'd done.
You can't knit the left sock first. Ever.