Little things do make a big difference:

Investigators continue to hunt for clues to the cause of the outage that cut electricity from east of New York, north to Toronto and west to Detroit, Michigan - an area home to about 50 million people.

Gent said the exact cause remains unknown, but indications so far point to a downed 345,000 volt power line east of Cleveland, Ohio, on the 'Lake Erie loop' - a series of transmission lines around the lake - as the source of the outage.

Within three minutes, starting at 4:10 p.m. Thursday, 21 power plants in the United States shut down, according to Genscape, which monitors power transmissions.

All that might be from one power line falling down (from CNN).