I've been an accountant for over 40 years and nothing surprises me anymore.
I've had loads of small business clients where the proprietor never opened bank statement envelopes so hadn't the foggiest idea how much was in the bank. Others who were owed tens of thousands because they never bothered checking/chasing customers who hadn't paid their bills. Some of these were professionals!!
The "best"/"worst" was an IT contractor who was paid every 4 weeks (not monthly), and completely missed that one payment from his agency had not been paid - I only noticed at the year end when I expected to see 13 payments and there were only 12 - there was still one per month which is presumably what the client saw on his bank statement. The amount "lost" was huge - something like £15k that he simply never noticed he hadn't received!
Same with individuals, as I'd often get a carrier bag full of unopened letters from banks, pension firms, HMRC, etc to prepare someone's year end tax return. These clients would just put all "brown" envelopes in a drawer or pile, never bother opening them, and just chuck them in a carrier to give to me once a year!
I remember a dentist client who wanted me to do a review of his financials for CGT and IHT planning. He hadn't a clue how much his pension fund was worth, didn't know his occupational pension age/lump sum, didn't know whether he had life insurance with his mortgage, didn't know if his mortgage was repayment or endowment, didn't know if the house/mortgage was in his sole name or joint names, "thought" he had some money in a building society, but didn't know how much and didn't know what kind of account it was (i.e. ISA or otherwise) and couldn't even tell me which building society it was. We finally agreed that he'd "find" the paperwork and give it all to me to look at. A few weeks later, he turned up with two huge boxes of "brown envelopes", most of which were unopened. It took many hours to open it all and sort it all out before I could even start to organise it into what was relevant, and start to write the report!
I really dread to think about the mess that people today will find themselves in now that most things are online and there isn't a "pile" of paperwork languishing giving clues as to their finances. Today, there is a very real risk of someone dying and the executors/family never finding out just what they had if they don't know roughly what they had and don't know all their internet email addresses and have access to their emails etc. Yes, if you know they had, say, a Halifax bank account, the executors can get info from the Halifax, but if they didn't also know they had a Furness B/S account, they'd not know to contact the Furness - you can't contact every last bank, building society, pension firm, insurance firm, stockbroking/investment firm etc. As I say, at least in the old "paper" society, the family would probably find an old BT share certificate at the back of a drawer, but today, there'd be nothing like that for people who've been wholly "online" for the past decade or two!