I once started writing a very long reply to someone's comment, but in the mean time this XKCD came out. It did an excellent job of draining my motivation to finish it (it wasn't literally an argument about "literally", but the general principle of the joke still applied). I actually still really want to reply on some level but it's possible I never will.

I think at some point you realise you're only arguing with one person and the whole argument is really a waste of time even though you're compelled to continue it until it's resolved. Blaming XKCD aside, getting burned out and never finishing the reply is something that's not quite on the list. It's close to "They disagree and are planning to write up the reasons later", just without "later" ever coming, and it's also close to the suggestion attributed to Airedale but without making a conscious decision.