piece of paper, I'm sure you have faced the issue of finding an invoice or some paper on which you have written a phone number and now can't find it.
I keep my diary really safe so if you are that kinda person, I would suggest a diary over a piece of paper and please write using a BALL Point Pen
why would a diary be any safer than a piece of paper? they made out of the same material. plus if anyone ever finds your diary, there will be no doubt that it's something to read through. because it contains personal information. private stuff.