There is always some reason behind whatever we do - something motivates, drives us. In 'revenge' films, the whole movie might be about a man who tracks down and exacts/takes revenge on the hijackers who shot his wife and children. That's his motivation. Think about any murder mystery films you have seen, and think about why the murder was committed - what the murderer's motivation was.
I sometimes think that motivation as a driving force in human behaviour has lost its 'drive'. Like a man who has just had sex and just wants to roll over and go to sleep, motivation is all pooped out/exhausted/run out of steam and it, motivation, just hasn't got what it takes to 'motivate' people any more.
Sometimes I wonder if many of them (I assume 'them' refers to the screenwriters who write the horror/slasher/torture movies) read the above passage from Amis's Money and took it to heart (that is, they agreed that their villians didn't need to have any profound or even viable reason for their crimes). From (the movie) "Seven" (1995) to "Saw" (2004), all the movies written and released in between those years, and probably from now on into the future, the motive-free thriller-horror movie has been a boon/a godsend/blessing in the sense of a tremendous advantage) for morbid, sunlight-deprived would-be Hollywood players who are more at home expending their energies on interesting and scary and original ways to kill people without bothering about coming up with any sensible viable reason why they are committing these crimes.
Student or Learner