as technical experts in this case before the constitutional court. we have also authorised the disclosure of our extensive explanation on proportionality that we submitted to the court of justice as well as excerpts from minutes of governing council meetings. the german authorities have assessed the pspp as proportionate before the constitutional court. with the new documentation, they are in a position to further corroborate their initial finding if necessary. our authorisations respect and are consistent with the independence of the ecb and the deutsche bundesbank, the fact that the bundesbank is an integral part of the eurosystem, the primacy of eu law and the binding nature of judgments of the court of justice of the european union. and they are in the spirit of european cooperation. i see no obstacle to the bundesbank continuing its purchases under the pspp after 5 august. and i trust that my german colleagues share the spirit of european cooperation and will continue 1 / 2 bis central bankers'speeches with their pro - european and constructive track record. 1 federal constitutional court ( bundesverfassungsgericht ), judgment of the second senate of 05 may 2020 – 2 bvr 859 / 15 -, para. 111. 2 judgment of the court ( grand chamber ) of 11 december 2018, weiss and others, c - 493 / 17, eu : c : 2018 : 1000. 3 account of the monetary policy meeting of the governing council of the european central bank held in frankfurt am main on wednesday and thursday, 3 - 4 june 2020. 2 / 2 bis central bankers'speeches

must be careful not to disturb this balance. and here is where i see some cause for concern. regulators might be tempted to lay down rules to cover every eventuality – think of the example i just gave you. and their motivation would certainly be laudable. but their goal would be unattainable. it is just not possible to cater for every potential situation. there are too many possibilities, most of which we cannot anticipate. no one knows what financial innovations might emerge ; no one knows where technological change will lead us ; and no one knows how the economy will evolve over the coming decades. if we try to cover everything, the rulebook will, at some point, become too detailed, too big and too complex. from that point onwards it will stop making the banking sector a safer place and instead create new problems. first, overly complex rules facilitate regulatory arbitrage. yes, we could add page after page to the rulebook, setting out detailed rules, definitions and thresholds governing how banks should deal with risks and specifying, for instance, which tools supervisors should use in certain situations, and when. but with each new page, more loopholes open up. it becomes easier for 2 / 4 bis central bankers'speeches banks to game the system. this defeats the purpose of a rulebook and poses a threat to stability. second, there is the problem of interaction. the more rules there are, the more they can interact and interfere with each other. if there are two rules, there is just one way in which they can interact. if there are 1, 000 rules, they can, in theory, interact in at least 500, 000 ways. it becomes ever more difficult to foresee the overall effect of the rules, and the danger of unintended sideeffects increases. and third, there is the issue of costs. the thicker the rulebook, the more expensive it becomes for banks to comply with it and for supervisors to do their jobs. these costs are justifiable if each additional rule reduces the risk of another crisis. however, at a certain point the costs of the rules begin to outweigh the benefits. so, instead of having overly detailed rules, we should have a strong basic set of rules that allows supervisors some discretion.. supervisors have the relevant skills and experience, and in - depth knowledge of the banks they supervise. we should ensure that supervisors can continue to apply their judgement. they should be empowered to assess the