Pride Goes Before A Fall
Mr Shaitana is filled with pride and extremely vain about the dinner he has put together. He believes he is the puppet master and his assembled guests his puppets, and is vain enough to think he has outwitted everyone, taunting them with insinuations about their various crimes. This vanity and pride leads him to let his guard down, ultimately enabling the murderer to add him to their list of victims. Pride causes him to underestimate the people he has gathered together and leads to his demise.
Not All People Who Kill Are Murderers
Although Mr Shaitana believes he has assembled a quarter of murderers, his failure to discover all of the facts about each of their crimes means that although all four have killed someone they are not all psychopaths or murderers. Major Despard has, by his own admission, killed a man, but far from having murderous intent, his intent was actually to save the life of a feverish man wandering into the dangers of the jungle; interference from his wife caused a chain of events that meant he accidentally shot the man dead. This does not make him a murderer and he is still far from the character of Dr Roberts, a genuinely dangerous serial murderer. We see the difference in their character and deeds also in the way Poirot deals with them both, highlighting that although each of them has killed, there are many differences in the intention of their action.
