Coups oust six times more autocrats than revolutions, while causing three out of four failures of democracy. Conventional wisdom holds that coups are, first and foremost, motivated by macro-organizational interests of the military. In contrast, we argue that personal interests drive individuals' active involvement in illegal power seizures. To explain why and which individuals conspire against their governments, we study the career prospects of individual officers. We expect that officers with little chance for promotion participate in coups to force their way up within the military organization. Using original data on all 7,400 serving officers in Argentina (1950-2007), we analyze biographic differences between all 480 coup plotters across the country's 18 coup attempts and the entire officer corps. We find that officers stuck within the military hierarchy and threatened with retirement were more likely to participate in coup attempts. The study demonstrates how organizational backlogs motivate soldiers to turn against their political leaders. This has implications for understanding the internal dynamics of political conspiracies, bureaucratic sabotage, and regime breakdowns.