Why autobiography is a lie

I could never write an autobiography because if I did, 90% of it would be complete bullshit. It's memory, man. As in, I have a lousy one. I don't understand how anyone could possibly remember events from a week ago, let alone from childhood. It doesn't help, in my case, that I spent a great part of my later teen years and early twenties completely whacked out of my mind on various illicit substances-- not the sort of thing that lends itself to perfect recall. I shudder to think of all the brain cells I snuffed out.


But in place of actual memories, I've managed to create my own private mythology, based loosely on reality. I've sort of filled in the blank spots with speculation that may or may not be true. My eye, for instance; when I was about three, I had a bad accident that damaged my right eye. I have no memory at all of the event, but I've created a story about it based on what I've heard from my Mom and various other sources and my re-imagining of it has become so clear in my head that it's almost exactly like a memory. 


So that makes me sort of wonder about the significance of actual memory. If something "untrue" can be as vivid in your mind as something "true", then what good is "true"? Like most writers, I live mostly inside my head anyway, yeah? Another example: dreams. Ever have a dream so vivid that you remember it years later? You remember it just as well, if not better, than something that actually happened? 


If memory is only a chemical reaction in your brain, a response to some sort of stimuli, then who's to say that there's any real difference between the "actual" and the "dream"?


So yeah. My autobiography would be equal parts real and unreal, and both parts would be equally valid. Because your life in your head is just as significant as the one outside. Maybe even more so.