The crux of his post is this:
[S]ometimes repetition is ineffective in promoting learning. … [U]nder certain circumstances … [repetition] not only doesn’t help, but could even impair your recall.The first such circumstance is repetition without attention or more elaborate processing of the material. He begins with the example of Americans and the U.S. penny.
[M]any of us [Americans] have seen [the penny] enough times to know every detail on it, yet we only pay attention to its brownish color to differentiate it from other coins and thus that’s the most we remember about it. If I were to give you an old roman denarius, and tested you a week from now about details on it, you would be better at it than what you can currently remember about a penny (it would be the same with the currency of any other countries than the USA).Is this example accurate? For you Americans, try to recall what's on the penny, and then compare it with what you find here. For non-Americans, try to do the same with a very common coin or bill in your country. How'd you do?
I did a lot better than his example would suggest. In trying to recall the Lincoln Memorial penny that was produced from well before I was born until 2008 (I don't recall ever seeing the newer union shield penny), here's what I could recall before seeing it at the link above: Lincoln's profile on the front (I couldn't recall the direction he was facing), some words above him, the year to the right of him, the Lincoln Memorial on the back, some words both above and below the Lincoln Memorial, and, on both sides, a raised ridge around the circumference. I could also recall that the outer edge was smooth, as opposed to the ridged edge on the dime and the quarter. I guessed that some of those words that I couldn't recall were "In God We Trust", but I can't fairly say that I remembered that. If my recollection is typical, I'd say that his example isn't the greatest.
That said, the point does not seem to be an unfair one. And he backs it up with some info on rote memorization:
In many experiments, where participants have to repeat items aloud over and over[, w]hen they are given an unexpected memory test on the rehearsed words, there is almost no relationship between the number of overt rehearsals devoted to an item and later memory. Simply repeating an item over and over has little benefit for memory in the absence of attention or more elaborate processing of the material.Remember all those rote repetitions you did back in your language classes? Yeah, that's about how useful they were.
The second such circumstance that he sets forth is when you've got to memorize multiple sets, say, Set 1 and Set 2, and each of those sets have multiple but overlapping items, say, A, B, C, and D in Set 1 and C, D, E, and F in Set 2. If you study Set 1 first, you'll have more trouble recalling that Set 2 also contains C and D because they are also included in Set 1. Why? Because "[i]f an item has been presented in several contexts, it may become difficult to retrieve the occurrence that is being tested". That makes the earlier repetitions of Set 1 detrimental to the later repetitions of Set 2.
How to resolve that problem? Gérman suggests using associative techniques. I'd put those items together; seeing a graphic of Set 1 right next to Set 2 would make it easier for me to associate and remember the differences.