when the big test comes, there are no hints

R' Shteinman records that R' Moshe Landinski, RY in the yeshiva in Radin, once told the Chofetz Chaim that he was reviewing mishnayos by heart while travelling and got stuck on a certain mishna that he could not remember exactly.  When the wagon stopped by an inn between villages (I imagine this was the 19th century equivalent of rest stops on the NJ or NY Turnpike), R' Moshe asked the Jewish innkeeper for mishnayos, refreshed his memory, and was able to continue learning.

The Chofetz Chaim remarked that this works on olam ha'zeh, but when we get the big test in olam ha'ba there will be no rest stops to pull into to take a break and refresh your memory!