Arthur C Clarke in his book '3001' has someone expressing surprise that no-one can explain the origin of the expression 'to know something like I know the back of my hand'. I doubt if I could recognise the back of my own hand from a given selection, so does anyone actually know the origin of this phrase?
Click here for an answer I gave to a similar question in the past. At least it shows I agree with you that such hand-back recognition is doubtful.
When this question has appeared before - as it has done many a time - everyone always seems to disagree with me, assuming they could do so easily. Perhaps if one is old with an easily recognisable pattern of liverspots or whatever...yes. Otherwise...no.
As to the origin, I'd guess it is no more than a bit of almost proverbial folk-wisdom.