knitting is so instructive

For reasons that are not clear to me, 2-1 = 2 when I was working on the clapotis while on the plane yesterday. I was just starting a row where I'd drop a stitch (on purpose), and I realized that I had 2 stitches before the stitch-to-be-dropped (aka stbd). And I can clearly remember having the appropriate number of stitches 2 rows prios, and I am certain that I purled 2 stitches together the row immediately prior. The lesson - when you are on a plane, because of the lower atmospheric pressure, the amount of oxygen available to your brain is decreased. Which can lead to hallucinations or muddled thinking. Neither of which mix well with knitting.