Spies come in many shapes. Some are motivated by ideology, politics, or patriotism. A surprising number act out of avarice, for the financial rewards can be alluring. Others find themselves drawn into espionage by sex, blackmail, arrogance, revenge, disappointment, or the peculiar oneupmanship and comradeship that secrecy confers. Some are principled and brave. Some are grasping and cowardly.

(Macintyre 2018)