It feels juvenile to hide it when I know no one will care, but the idea that it can be entirely personal opens the option to being more honest. Future self can still be judgemental, but the only way to avoid that is to pipe it to /dev/null instead.
Edit: I had a handwritten journal once when I was 13 or so, it disappeared, probably my mom finding and reading and destroying it. Just do it on a computer. Besides for me I can barely stand handwriting anything longer than a page anymore.
That is the most awful thing I've read today.
I snatched that from GoodQuotes. I'm no poet, but I feel like it carries a lot of truth. If somebody wanted to rob my house, if all of my most private thoughts and truths were stacked on the coffee table in the front room, they would still make off with my TV, and those books would still be sitting there when I came back to the aftermath.
I don't (yet) read it as quickly as I read normal English, though; if you're interested in self-reflection and review, this tradeoff won't be an obvious win.
I've seen Ford shorthand system which replaces alphabets with easier to write variants. It could also be used to write faster and provides some obscurity from the uninitiated.
Write honestly, review periodically, and discard what's really just mental or psychological dead-weight. It's surprising how much of that, once on paper, can be just let go and be done with.
I've used mostly moleskines for their range and availability, particularly the hard covers. Those all now have huge sections of sliced out pages so I'm trying their Valence line where every page is perforated.