[lhh]

He mentions several times that accountants do their work in Excel, but any account would consider it barbaric to actually try to do transaction-level double-entry bookkeeping in Excel instead of a purpose-built system like QuickBooks/Xero/NetSuite/etc. I think I've also probably seen more broken financial models than logically sound ones in Excel, so the integrity of spreadsheets is oftentimes not even safe in the hands of finance professionals.

Data integrity is definitely a hard problem.