Retrospective falsification is the unconscious distortion of past experiences to conform to a person's needs in the present. Human memory is very malleable and can easily be hidden or distorted for any number of reasons.
For example, an adult suddenly "remembers" being sexually abused as a child. The questions that need to be asked are "Is this a case of repressed memory?" or "Is this newly-found 'memory' the result of a planted suggestion?" Experiments with planting false memories through hypnosis have been conducted and have shown significant results. These studies involve 'planting' harmless memories (like going to Disneyland and meeting Bugs Bunny) in the participant's memory.
However, false memories can also originate through dreams or through other outside suggestion. This is why practitioners must proceed carefully with memory work because memories are not always completely reliable. This ability of the brain to distort and/or falsify memories can make the investigation of a client's past challenging.