The health of individual banks depends not only on supervision, but also on the overall economy and the structure of the banking system; and the ECB’s influence on that is limited. And we should not forget that irrational exuberance, as can be found ex post in many a “bubble”, is simply part of human nature. That’s another lesson the crisis should teach us.
Much has indeed been done to harmonise regulation, both in Europe and worldwide. Just think of Basel III and the single European  BIS central bankers’ speeches  1  rulebook. Particularly in Europe, the European Commission and the European Banking Authority (EBA) have also contributed to a harmonised regulatory framework by adopting Regulatory Technical Standards and by issuing guidelines and opinions.