The marathon coverage of the Boston Marathon bombing has set into motion the all-too-familiar. When something awful happens, the human impulse is get informed instantly. That often means rushing to a TV and gaping at the unfolding drama. It’s an understandable reflex, but usually, a self-defeating one, like scratching a sore or drinking sea water.

It may satisfy the immediate urge, but beware the consequences. CNN’s false report about arrests was as predictable as it was irresponsible; live TV coverage is a world of blunder. So, if you must tune into 24-hour cable news for the latest, there a few things always to bear in mind:

A watched pot never boils. Following violent crimes and disasters, the intensity of the coverage is inversely correlated with the prospects for advancing the story. Incidents last as long as they last – usually, seconds – then they are over. The ‘when’ and ‘where’ and some of the ‘who’ (victims) are immediately obvious. The rest of the ‘who’ (the culprits, the missing), plus the ‘why’ and the ‘how’, can take days or weeks or months to unravel.

The latest developments usually aren’t. Desperate to add to the endlessly repeated basic facts, reporters will breathlessly pass along tiny […]