For quite a while I just to have digital personal diary. First as a text file stored in my computer, occasionally backed up on cd. Then I switched to ohlife.com. I liked the clean interface and the fact that you'd get reminder mails you could just reply to create a new entry. Most of those reminders I just deleted I noticed. Ohlife shut down last year. Fortunately the creators allowed you to download a backup of all your entries so no content is lost.
Since then I don't keep a personal diary. I do post occasionally on twitter as well as lots of other social media or as it just to be called word wide web. My calendar is on google, just as my mail and part of my documents. Besides that my photos and other documents are stored on my own laptop - not stored on any cloud (at least not that I know of), but synced via syncthing in case I lose my laptop. I create notes on evernote, store articles I might want to read on getpocket, and sometimes publish code on github, bitbucket or other hosted code services. And of course most of my activity is tracked by Google, Facebook and probably other organizations I know or not know of.
All in all a lot of digital data or information by or on me, created on purpose or by accident. All those information combined would be enough to reasonable 'auto-create' a diary entry.
Some new online diaries I just found on the interweb allow integration with twitter and facebook such as Journalate. But I don't want to use on online diary anymore that stores data on it's own server(s), certainly not one that only allows you to download your entries if you pay them money. I'd rather have my diary stored on my own computer, or maybe on some blockchain, but only accessible by me. Also my hypothetical diary doesn't need to contain a copy of all that data, a link to that data combined with some tags or notes created by me would be could enough.
I wonder if something like that already exist?