Stirlingitis is a terrible afliction affecting many engineers and mechanics who have enjoyed working with the stirling engine. Many who have contracted this condition of being addicted to tinkering and playing with this curious mechanical device can't help themselves but continue to do it for life.
An engineer meets the stirling engine. He can't help but wonder "what if?" there are a million variables. Curiosity has taken advantage of him. He's hooked. He can't help himself. Hence the engineer has contracted "stirlingitis"