At first, when the germ of my story was a husband who discovers his late wife’s secret diary, the novel was called generically The Diary. But that plot line felt like too much melodrama (and what do I know about husbands?), so I replaced the husband with a hapless thirty-something single and the diary with a love letter trapped unread in a book for many months; the novel became The Letter. Of course later I added the diary back in to complement the letter, and I called the thing The Letter/The Diary.
This arrangement lasted me all of the first draft and into the beginning of the second draft, until this morning I decided to remove the letter altogether (what do I know about love letters trapped unread in books for many months?) but keep the diary, at which point the novel became the cumbersome formulation The Letter/The Diary.
That’s when I remembered the list of halfway-decent titles I had worked up a while ago (none of which really seemed quite right for the final title but one of which could certainly serve temporarily). I took the best one and gave the novel the working title The Long and Short of It. I’m sure that’ll change.