An aggressor nation or extremist group could gain control of critical switches and derail passenger trains, or trains loaded with lethal chemicals.

You know, as director of the CIA, I got an awful lot of intelligence about all the horrible things that could go on across the world.

Well look, CIA is an agency that has to collect intelligence, do operations. We have to take risks and it's important that we take risks and that we know that we have the support of the government and we have the support of the American people in what we're doing.

I think the primary message to the world is that the United States is going to remain the strongest military power in the world.

Nothing helps make a leader more approachable than admitting your struggles, screw-ups and behind-the-scenes thinking on hard calls. If the leader makes this a priority, the whole company will be more open and methodical learning from failure.

I've seen it again and again in my consulting: Most teams are too large to be innovative, despite their leaders' best intentions.

I urge North Korea's leaders to reflect on Burma's experience. While the work of reform is ongoing, Burma has already broken out of isolation and opened the door to a far better future for its people.

What I teach our people is that, as a leader, you have four key roles apart from people management. First is to champion the grand vision. Two, install systems and a culture to run experiments. The third thing is to savour surprises. The fourth thing is that even a leader's ideas need to be subjected to tests.