There are four major reasons that people forget information: storage failure, interference, retrieval failure and motivated forgetting. According to most of these explanations, forgetfulness can result due to the way information is stored in the brain or how different memories affect each other.
Storage failure occurs when information does not enter long-term memory. For instance, if a person pays more attention to an object’s color and size than to its shape, the detail of the object’s shape may not enter the long-term memory.
Interference theory proposes that the brain may not be able to recall certain details due to the existence of other similar details. The two main types of interference are proactive interference and retroactive interference. Proactive interference occurs when a new memory is difficult to recall due to the existence of a similar older memory. Retroactive interference is when newer information makes it difficult to recall older information.
Retrieval failure is the inability to locate a specific memory though it is known to exist. Decay theory is one possible explanation for retrieval failure. This theory suggests that a memory trace is created with the making of each new memory, and as the memory trace fades with time, it eventually vanishes if the memory is not recalled.
Motivated forgetting theory suggests that an individual does not recall certain memories because they are traumatic. Suppression and repression are the two fundamental types of motivated forgetting. Suppression occurs when an individual consciously forgets, and repression refers to those times when an individual forgets on the unconscious level.