Asked by: Alireza Riasati, Iran
Multiple explanations have been proposed. We may forget because we didn’t store the memory effectively in the first place. It is also possible that memories decay over time. As they have not been revisited, their biological ‘trace’ becomes weak.
Another theory suggests that new memories can interfere with older ones. Or that memories have been encoded and stored but that there is a problem with retrieval. Scientists sometimes refer to ‘motivated forgetting’ too, which involves forgetting an unwanted memory such as a trauma. This is controversial as there is also evidence that such unwanted events may be particularly difficult to forget.
Forgetting is not always a bad thing! It would waste cognitive resources if we remembered every last detail of the world around us.