If your grew up in the shadow of the cold war at some point you were exposed the civil defense that instructed the viewers that during an atomic attack that they should, the moment they see the flash, duck and cover into safety.
This advice has become roundly mocked as useless and is often referred to when someone thinks that an authority is proposing a solution that offers no benefit. This is another example of cynicism masquerading as wisdom.
It is true that if you are close to a nuclear explosion ducking and taking cover will do you little good, but if you are truly close you will have at the chance to take such action. The advice is aimed at person who is distant enough that they can see the flash but where the blast is delayed. In that event, taking cover is flipping brilliant.
A few years ago a meteor impacted the Earth over Siberia exploding with the force of hundreds of thousands of tons of TNT. Only the shallow angle of its approach kept the destruction from becoming catastrophic. However scores of people were injured in the blast, and most because they did the exact opposite of ‘duck and cover.’
They saw the flash of the meteor, they rushed to the windows and stared, and then the blast wave arrived, shattering the glass and injuring them.
Sadly with the situation in North Korea and the United States atomic anxiety is on the rise and yes if you are near ground-zero of a detonation the flash and the blast will be nearly simultaneous but if they are not you would do well to remember Duck and Cover.