6 ideas
Memory failures fall into three sins of omission (transience, absent-mindedness, blocking), where information is unavailable when needed, and four sins of commission (misattribution, suggestibility, bias, persistence), where something is present but wrong or unwanted. Separating 'failing to retrieve' from 'retrieving distorted or intrusive content' lets each failure be traced to its own mechanism instead of treating forgetting as one thing.
The seven sins are not design flaws. They are side effects of features that usually serve us well. Transience clears out information we are unlikely to need, gist-based storage makes generalization possible, and persistence keeps threatening events available so we avoid them next time. A memory that recorded everything verbatim and permanently would work worse for a creature that has to act in a changing world.
Absent-mindedness happens when attention is elsewhere while something is being encoded or while a planned action should be retrieved. The information was never properly stored, or the cue to act came when no one was looking for it. Forgetting where you put your keys is usually not decay: the placement was never attended to in the first place. Prospective memory lapses are best fixed with distinctive external cues present at the moment of action.
People often remember the content of an experience correctly but assign it to the wrong source, time, or place. The result is false recognition, cryptomnesia (unconscious plagiarism), and confident witnesses identifying an innocent person they saw in a different context. Familiarity is dissociated from memory of where the familiarity came from, and the feeling of 'I know this' gets misread as evidence of a specific past event.
Memories can be altered or created by misleading information, leading questions, and repeated social pressure introduced after the event. Recovered-memory therapy and coercive interrogation have produced vivid, confidently held false memories. Because retrieval is reconstruction rather than playback, information supplied after the fact gets built into the memory. How the recall is prompted is part of what is remembered.
Bias means current knowledge, beliefs, and feelings reshape how we recall earlier ones. Consistency bias makes past attitudes seem closer to present ones, and change bias exaggerates past difficulty so that present improvement looks larger. Egocentric bias recasts our past selves more favorably. Read an autobiographical memory as a statement about who the person is now, not a neutral record of who they were.