"Cows are not designers."

Steven Pemberton has published an excellent article on the weaknesses and short-comings of HTML5. There are many. But aside from that, for those who have no interest in technical musings, it contains a section that is true capital-L Literature. This describes something we talk about in Information Technology all the time [or at least we should be!] as well as in transportation advocacy. Just read it, it is brilliant.

Cows are not designers.
Cowpaths are data.
If you pave cowpaths, you are setting in stone the behavours caused by the design decisions in the past.
Cowpaths tell you where the cows want to go, not how they want to get there. If they have to take a path round a swamp to get to the meadow, then maybe it would be a better idea to drain the swamp, not pave the path they take round it.
Paving cowpaths is a bad design principle.

Truth. I imagine there are many circumstances and fields where this is applicable.