My dad kept a diary during his WW2 duty. In his 80's, he read it and was shocked to discover it did not line up with his memories.
In all seriousness it's crazy how bad memory is. Like we all have a false version of the truth.
The second part was just me agreeing with their comment that it's crazy how bad our own memory is and how it's difficult to come to grips with. Like when my mom, sister, and I are all arguing over a past event and remember it very differently. The true events are (to my knowledge) absolute, but in a philosophical sense, we're all living in our own reality as our memories are telling us the events unfolded differently even though they didn't.
I sometimes keep a diary, for example when I go on long trips that are different from my day-to-day life. I try to be as accurate as possible, but sometimes i notice what i write isn't fully representative of my state of mind at the time, simply because when you're writing stuff down (especially when you're writing with a pen and paper (slow!)), you can never fully capture all the concurrent thoughts and emotions you're experiencing, so its impossible for a diary to be fully accurate. Undoubtedly, e.g. Elizabeth Loftus has done a lot of prominent research in that field, our memories tend to be fallible, but maybe that's part of the reason?
When I was writing a paper on the history of D, I had kept a lot of records, such as emails. I was often surprised when the details didn't quite line up with my memories.
This is one reason why one cannot get a fair trial 40 years after the fact, if any of it relies on eyewitness testimony.