REUTERS/Toby Melville Britain's Chancellor of the Exchequer, George Osborne, delivers a keynote address at a dinner held by the CBI (Confederation of British Industry) in central London May 20, 2015. 
It's to do with proving a manager's guilt when a scandal, like rate fixing manipulation, hits a bank.
The so-called senior managers regime, which comes into effect next year, was designed to make top bankers prove they did everything they could to prevent bad conduct.
But a U-turn from the Treasury on Thursday means the burden of proof now falls onto regulators, who will have to prove they did know something was wrong.
Senior managers will still be required to show they behaved well, but now it's a "duty of responsibility" to do so, rather than a "presumption" that they didn't. The three-word change makes all the difference.
The rule in its previous, tougher form had worried a lot of banking executives because they were concerned they would end up on the hook for scandals at their bank - even if they couldn't have possibly done anything about it.
Barclays even warned board members to challenge people who were making an "unusual" amount of money, because of the likelihood that the high profits would come from wrong-doing.
The Bank of England played down the change.
"This change is one of process, not substance. The focus for firms and individuals should be on complying with both the letter and the spirit of the rules rather than considering ways to circumvent them," said Andrew Bailey, the UK's top banking regulator and a deputy governor at the BoE.
This may be true, but, in the case of the senior managers rule, the process and the substance were the same thing.
The way the rule was to be enforced - by getting bankers to prove innocence rather than having a more poorly funded regulator try to find them guilty - was the whole reason it was taken seriously by the banks in the first place.