This explanation has always seemed a bit daft to me. > If it had been common knowledge among castle builders, then why are there still quite a lot (about 30%)

This explanation has always seemed a bit daft to me. > If it had been common knowledge among castle builders, then why are there still quite a lot (about 30%) of castles with counter-clockwise staircases? AKA it's almost surely just a builder's preference probably stemming from their handedness.