When you are
studying for an exam and as soon as moving on to the next
definition/topic you're studying, you forget the prior thing that you just learned/memorized. Analogous to playing the arcade
game "wack-a-mole"--once you hit one mole, another pops up.
When I was
studying for my archaeology test I finally memorized the information for Tenochtitlan, but then
forgot all the information I learned for Machu Picchu. The wack-a-mole effect
failed me again.