I suppose this episode attempts to tackle the subject of false memories: Memories that are actually planted or created during the process of ‘uncovering’ something repressed. It’s a dark, serious topic, and “Retrospect” tries unsuccessfully to delve into the complicated matter. There’s a lack of clarity in the approach – I’m not really sure the ‘false’ (I guess?) memory is even the product of The Doctor’s attempt to find the repressed information. Also, because the Doctor is the one unwittingly doing the planting there isn’t much nuance as to his motives, (we know he’s a good person) so it’s all basically just a horrible accident.
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It bothers me a little bit that there was never really an explanation for Seven’s memories, yet they seem to decidedly come down that she was wrong. This isn’t handled confidently at all- either give the audience more of an indication how her memory could be false, or really commit to the verdict being unclear, as well as the fallout from that lack of clarity.