Thoughts

It can be argued that most of our memories are not 100% the reality. There are gaps and biases in our perceptions and inaccuracies when converting one concept to another (like pictures to words). Even our vision contains several blind spots that we don't notice because our neural networks (brain) automatically fills in the missing sections with self-generated 'stock images'.

This varies from person to person and generally becomes more pronounced with time. The Nelson Mandela is quite normal and becomes an issue once people stick to the believe that only their perspective is infallible; or if it leads to extremely inaccurate conclusions due to false memories.