When the Sunday Psalms are appointed for Prime and the Little Hours, that means in large part - literally - the reading of Psalm 118 (Beati immaculati in via), that hymn to righteous obedience, divided into eleven parts*. Now, for some time now I've been making what seemed a mysterious mistake: at Sext, once I'd read the first verse of Psalm 118 part viii, I'd turn the page, expecting to say Septies in die laudem dixi tibi... (Ps 118:164) but find a different verse instead - for that line doesn't crop up till None, when it is the fourth verse of Psalm 118 part xi.
Why this weird error? Well, it wasn't until I'd been tripped up by this confusion several times that afterward I went back to see why this was tricking me, and found that the verse I'd just read at Sext was Iniquos odio habui: legem tuam dilexi (Ps 118:113), whereas at None the verse actually preceding Septies is Iniquitatem odio habui, et abominatus sum: legem autem tuam dilexi (Ps 118:163) - it turns out the verse at Sext is almost identical to the one at None, hence my mistake.
(* At Sunday Prime, the first psalm to be said is Psalm 117, appropriately enough of course, whereas at festal Prime it is Psalm 53, and thereupon one begins Psalm 118 parts i and ii; I've long thought that, owing to its twin themes of sunrise and of love for God's Law, it would be good to instead begin Prime with Psalm 18, as has in fact been used at Prime on Monday since St Pius X's reform of the distribution of the Psalms in the Breviary. I remember when making a retreat at Tarrawarra Abbey taking a very long walk, with a psalter in hand, and reading Psalms 18 and 118 in one go...)