In 1873, Walter Bagehot wrote that "the business of banking ought to be simple; if it is hard it is wrong." He would have struggled to recognize today's banking system.

It is not just ever more ornate derivatives that bend the mind. Financial firms themselves have become fabulously complicated. Citigroup lists 2,061 subsidiaries and affiliates while the institutional chart of JPMorgan Chase is 267 pages long.

Complexity -- as Bagehot predicted -- has become a curse. If nobody can understand financial firms, they will become ever more accident prone.

The crisis that exploded a year ago offered a salutary lesson in the dangers of complexity. Many shareholders and creditors simply did not fully comprehend their investments. Instead they were forced to trust managers and the rating agencies.

Regulators too could be forgiven for scratching their heads.

"Supervisors are at a decided disadvantage in understanding risk-taking and compliance for firms that might involve dozens of jurisdictions, hundreds of legal entities and thousands of contractual relationships," former Fed official Vincent Reinhart has written.