sospan, I do those sort of things all the time, with or without a head injury I have just cut birthday wrapping paper too small, now it doesn't fit round the gift and I've run out of paper Mrs Bouquet
There was the OCD episde - Obsessive Celery Disorder. As part of my rehab, I had to relearn how to cook. When I was following a recipe I was preparing the vegetables one part required some celery, I knew we had some but couldn't find it, hunted high and low couldn't find it. My wife took me to a local supermarket to get some celery. Going around was a struggle but got some bits and pieces, paid and put them in the boot. Just as we were leaving the car park, I realised that I had forgotten the celery.
So rather than turn back my wife called in at a small convenience store and bought celery. When she went to put it in the boot, top of the shopping from earlier were two packs of celery ! To make matters worse when we got back to the house, next to the chopping board was a big pile of celery - I had forgotten that I had cut it, hence there were no more in the veg rack when I looked.
as Homer says Doh, Doh, Doh!