Interesting question because it makes you consider what you have forgotten in your life and why.
My view has always been that you forget things due to lack of reflection. The mind remembers because you remember if that makes sense. If you think back to your childhood a lot, to certain parts of it, it's unlikely you'll ever forget those parts. If you, however, have a part of your childhood which you'd rather not think about, you're likely to forget unless you subconsciously think back to it.
Another aspect, is that the stronger an emotion at the time was, the more likely you're to remember it even if you don't actively maintain the memory. A friend's death, moving homes, an accident, some great movie you saw on TV, etc.
But, of course, the huge majority of things we forget are the casual memories: going to school, homework, etc.
Anyway, to the question: I don't think I have forgotten that many vital parts in my life. A *lot* has happened in my childhood years which I wish I could have forgotten but I can't and as a teenagers, I had to carry the burden of those memories with me. In fact, I wish I could remember more of my earlier childhood - when I was 5-7 years old, just before the whole mess started. A lot of my memories from back then got murky due to the events of the years that followed. Thank god I still have lots of photographs and slides from those earlier years to refresh my memory or to even rebuild it (a memory is rarely completely gone).
