Imagine you can travel back and forth in time. You arrive at a job site 30 years in the past and tell your helper, "Grab the cordless rotary hammer and set up the laser level while I call the lumberyard on my cellphone." He'd probably ask what you'd been drinking.

Next, leap forward 30 years from now and ask your sidekick to roll out the extension cords. Chances are, you'd get the same reaction.

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