why do people feel the need to buy expensive cable

Mr Self does not need ESP. He has a first class honours degree in engineering from Cambridge University (i.e the top 10% of his year) and then psychoacoustics at Sussex University. For years he worked with audio legend Peter Baxandall and a number of well known electronics manufacturers. He holds a number of patents on electronics design and is the author of a classic book on amplifier design. Geoff I cannot help it if you have never heard of him.
This is what he wrote on the directionality of cables: "Cables are directional, and pass audio better in one direction than the other."
Audio signals are AC. Cables cannot be directional any more than 2 + 2 can equal 5. Anyone prepared to believe this nonsense won't be capable of designing amplifiers, so there seems no point in further comment.

willemj, why are you arguing against your own star witness? You quoted him as stating cables are directional. Did you misquote him or are you just confused? 😳

The quotation marks are his, to define the position he wants to argue against. His own view comes with the words Audio signals are AC.....
I am afraid I created some confusion. What I should have writen is:
against the view that cables are directional, Douglas Self answers ' Anyone prepared to believe this nonsense won't be capable of designing amplifiers, so there seems no point in further comment.'

Oops....standby willemj for being chastised for "Appealing to Authority!"

Sure, and very good authority it is.