On the One Hand ...

In Iris Murdoch's first novel, Under the Net, the narrator quarters himself and a sidekick on the philosopher Davey Gellman. We see Gellman at work

... writing an article for Mind on the incongruity of counterparts. He had been working for some time on this article, which he wrote sitting in front of a mirror, and alternately staring at this reflection and examining his two hands. He had several times tried to explain to me his solution, but I had not yet got so far as grasping the problem.

 I have never written an article for Mind, nor contemplated doing so. Yet now and then I find myself writing queries in SQL and thinking of this, usually when I am combining a layer or two of inclusion. Time series can produce that effect too.