What Are The Odds?

This is from Steve Chapman over at Reason.com on the terrorist threat:

...after the Irish Republican Army failed in an attempt to blow up British Prime Minister Margaret Thatcher, it said, "We only have to be lucky once. You will have to be lucky always." Al Qaeda [...] faces a very different challenge: For it to carry out a nuclear attack, everything has to go right. For us to escape, only one thing has to go wrong.

The may be correct, but even if a nuclear attack were the only way to kill large numbers of people, the IRA quote above is still true.