Now we all know that the Clonetroopers are based off of Jango Fett who met his warriors's death at the hands of Mace Windu; what the books and graphic novels go into more detail on is how they were all trained by Jango, with some, ARC Troopers having even more extensive attention from him as well as less genetic variation from the original.
Jango was one of the Mandaloreans
, a warrior people who's galactic empire ambitions were defeated by the Jedi almost 4,000 years before, in what became known as The Mandalorian Wars.
One might think when they were indoctrinated with the potential for caring out Order 66 that they were more than ready for the task with the same mercy given to Jango by Mace. It would be interesting if there was a cut scene of this floating around somewhere, as I notice no one has questioned how quickly They turned, as the motivation must have seemed quite apparent, conditioning aside, compared to Anakin's.