Before sending/sharing important documents, please verify the address you've been given. Please don't just directly send/share it.
Once it's been sent to the wrong address, you've got to assume that it's permanently out there.
So someone shared more than 10 important extensive documents with me on google drive, which I definitely wasn't supposed to have.
Naturally my first instinct was to copy those files in case they were interesting.
Although I won't name anything in specific, there were definitely a lot of transactions and personal data in those files. I'll leave it at that.
In another case, someone mistook my phone number for their dad's and sent a long voice message wishing him a happy birthday. Must've been very embarrassing.
So the lesson to be learnt is to always send a message in advance and ask, hey is this "...'s" phone number? And also double check email addresses.