At one time, alphabetical order was something we were all used to using. When I was at primary school, we even lined up in the yard in alphabetical order of surname (an early lesson for me in alphabetical discrimination!) At secondary school we sat in that order in class: the friends I still have from school days mainly had surnames beginning with "P". If you wanted somebody's phone number, you went to the phone book, which in those simple nationalised days contained most people's numbers in one sequence, and you used your knowledge of the alphabet to find the right page. You were used to the idea that a page headed Allen-Atkins would include names such as Andrews and Ash. (All right, some people didn't get it even then, but it worked pretty well).
Times have changed. The phone book which popped through our door last week is a shadow of its former self. (It's still in alphabetical order, but it's not so useful now that so many people are not in it!)
Students give the impression that they are not used to alphabetical order, but as a parent I know that children do still get taught the alphabet. Younger children's classrooms still have colourful letters with pictures of things beginning with the appropriate letter round the walls in alphabetical order, just as we had. (You can even practise getting the order right here !) Perhaps it is more that students have already forgotten something they used to know, because it is no longer needed to the same extent in daily life.
The library catalogue is now in its death throes, with the new discovery platforms jettisoning the idea of linear lists arranged by alphabetical order. Internet searching has given us so many more ways of finding what we are looking for. We can't get rid of the concept that easily, though. Our books are classified using LC, which is based on the alphabet. P is a section, PR is another section, PS is another one again, and that is the order in which those sections are shelved. That second letter seems to cause a lot of confusion. Use the index to any book, and you are back with the same "phone book" principle. In an e-book you may be able to search for the term you want and find information without it, but the physical object still requires you to be able to use one.
Print periodicals, the actual hard copy physical objects (of which we still do have many, especially in humanities subjects) have to be arranged on the shelf, and traditionally that is in alphabetical order. Very often I have found people looking bewildered and saying things like "it's complete chaos", "it's not in any order" and even "why aren't they in alphabetical order?" They are, of course, in alphabetical order, but this sequence includes a further element, a large number of Welsh language titles, which throws people. "W" and "Y" are vowels, but they look strange to the uninitiated (which might include casual shelvers).
Then there is that nasty habit they have of changing their titles. Keep them together on the shelf in one sequence, say the academics - it's the same thing, it may have changed its title but everyone in the academic community knows it is the same thing. Well, fine on the shelves in your own study, perhaps, but if you try this in a large library it will soon come undone - every student and shelver would also have to be able to recognise it, and the only way round that is to complicate your acquisition process and add a whole lot of extra manual labelling (and it probably wouldn't work even then). (There's one glorious exception to this - Cambridge Medieval Celtic Studies became Cambrian Medieval Celtic Studies when its editorial team moved from Cambridge to Aberystwyth, apparently with a view to keeping it together on the shelf. Strictly speaking, the new title should come before the older one, but it really is close enough to work!)
Finally, there's that old problem of recognising that signage tends to refer to either end of the sequence but not to everything in between. In the card catalogue days, this meant knowing that a drawer which was labelled A-C would include B even if it didn't say so. Our end-of-shelf signs do much the same at the moment. I am toying with the idea of having a full shelf list at the ends of the shelves instead, for more clarity (in alphabetical order, of course!)