Only necessary if you keep your job. If you don’t, there are plenty of places you can live very nicely without having to explain where all that money came from.
Your neighbours will be too afraid you’ll wonder the same question about them.
And the only one you may need to explain yourself to is taxes; I have (had) colleagues working at the tax office, they're working on machine learning algorithms to detect suspicious activity on bank accounts (because the tax office has full access to everyone's transaction history, of course). They focused on suspicious repeat transactions, but I'm sure they will at some point focus on a suspicious absence of transactions, e.g. no grocery purchases.
That’s cool. Canada implemented some kind of suspicious financial transaction agency thing only in 2000 (to stop money laundering and TerRoRiSM) and just issued its first fines to banks this year.
While large volumes of transactions have been reported, the agency mostly… well, took reports!
It can be a hard nut to crack and I don’t think governments actually want to find and stop the transnational kind money laundering.
(because the tax office has full access to everyone's transaction history, of course)
In what country? It maybe possible for tax agency to request access to the transaction history in case of the audit, but I doubt they just get a feed of all transactions.
Your neighbours will be too afraid you’ll wonder the same question about them.