The problem with reality ...

... is that it doesn't fit neatly into the neocon ideology that calls for establishing American-style democracy by force and expects to be greeted with flowers by those invaded and occupied.

As this newly declassified document points out

Intelligence analysts predicted, in secret papers circulated within the government before the Iraq invasion, that al-Qaida would see U.S. military action as an opportunity to increase its operations and that Iran would try to shape a post-Saddam Iraq.

I don't think it was really that difficult to foresee the problems in a post-Saddam Iraq. But the Bush administration simply chose not to. Because it didn't fit into its neocon agenda. And thousands of lives later, Bush and his toadies still don't get it.