The Economist magazine has a story about the turmoil in the world of accounting standards. Near the end of the article it has the following quote

"None of this, however, will address the deepest flaw in accounts, says Baruch Lev, a professor of accounting and finance at the New York University Stern School of Business. This is the reality that most of the numbers in accounts are not facts but estimates. People are not good at estimating things, he says, and no amount of new accounting rules and auditing will change the fact that estimates are fragile and easy to manipulate. "