Wack-a-mole effect

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.