Final answer:
Andrew's issue with not remembering his third grade teacher is most likely due to decay of memory, which is the loss of memories over time due to lack of use.
Step-by-step explanation:
Andrew is likely experiencing decay of memory, which refers to the fading of memories over time when they are not used or revisited. In this scenario, because Andrew had not thought about the third grade or his teacher in many years, the details of those memories have become less accessible and have likely diminished.
This is a normal occurrence and can happen to anyone; as memories are not constantly activated or rehearsed, they can fade, leading to difficulty in retrieving them later on. Andrew's inability to remember specific details about his third-grade teacher illustrates this phenomenon of memory decay.