A lot of critical processes are just excel sheets that people open and run once in a while, maybe copy / paste or click a button in there, then close.
Some processes are automatized, but there is no way to check if the result is good. Best you can do is to have a human look at the numbers and say "LGTM" with some confident face and call it a day.
Said client handle billions of euros every year for other entities. They basically influence the entire world economy on a daily basis.
Now, get audited from top to bottom, from internal and external teams, and all audits pass eventually. I met mostly good people there that take their job seriously. But still, every time I dive deeper into their rabbit whole, I just can't believe what humanity stands on.