Terrorism and Investing

[SpeakEasy]

Immediately after 9/11, the markets dropped drastically, but recovered.

I have assumed that another major terrorist attack in the U.S. is inevitable, that it will be roughly on the same scale as 9/11, and it will have the same immediate but temporary effect on the markets. The only question, in my mind, is when it will happen.

A person could hold a significant chunk of cash in reserve for just such an event, to invest immediately after another attack.

Is this wrong?