I nearly thought I had lost a rather important blob of TeX that I had typed up in May, but it turns out it was hiding in a file named scratch.ltx in the directory I was working on the HyLo paper in.

This is, roughly speaking, the electronic equivalent of finding your passport nestled in a wad of papers in a pants pocket in the dirty-laundry hamper, only I had the advantage in this case that I could run find and find the exact right pair of pants by their modification date.