Hi, Caravaggio. Yes, I can identify with the problems of the carpet fitter.
I was cutting a carpet to fit into a corner, so thought I would leave a wide margin and then trim to size as I fitted the final few inches. Sadly, I was cutting from the back of the carpet. When working upside down, I get disorientated, and ended up with an overcut of about eighteen inches. Hence, the unsightly patch concealed by a bookcase.
Similarly, I have lain on my back under cars, furiously tightening bolts I am trying to undo.
Best wishes for now.
P