Amdahl's law (Score 2, Informative)

Some tasks can't be done in parallel and this is the Achilles heel of massive parallel architectures. See for instance http://en.wikipedia.org/wiki/Amdahl's_law. No parallel hardware and no parallel algoritms - no matter how clever - will help you, if you have a task of sequential nature (and even only help you somewhat no matter how massively parallel it is, if your task is partly sequential).

If one truckdriver can drive a truck 50 miles in one hour, how far can two drivers then drive the truck in the same amount of time?