We grow up and stop writing diaries. Thinking that's such a childish attitude.
But life keep it for us, inside the sharpest memories that we met. The ones that would remember every detail from the moment when we were together. Just to ask old friend, do you remember the b-day party when we were 16? and you will soon understand that what's in your memory is just a tiny piece. Unless you are the one with elephant memory.
But that isn't the only resource that life uses. Some of use keep what I like to call "miss tagged" diaries: notebooks from childhood, some special candy papers. The postcards we received on some special holiday (Christmas, Birthday, etc) The bank account statement (Yeah we need to, you never know), random paper record: like the one we saved when joining that old gym we aren't members any more.
Technology has develop and with it we have even more space to store, maybe this space is less tangible but it gives us a place to write, to save memories. Just glance at the mobile and find the saved sms. Or the email dated 3 years ago that for some unknown reason still is on your inbox (Or folders if you are more geek) And what about the newest of all: your preferred social media.
We keep writing our lives down, with the hope that one day if needed we would go back and find that particular memory. Sometimes, it would be the memory to find us when cleaning up the room, the email or the cellphone.
We might never need those memories, but thinking that there wont be a trace of our lives in this world is a hidden fear, is so hidden that we would never admit that we keep diaries, but we are unable to stop keeping information on all the other available forms.