Define "hard". Does it mean, you need greater knowledge? (communication models, deadlock/livelock, etc) Does it mean, you need greater attention to detail? (m

Define "hard". Does it mean, you need greater knowledge? (communication models, deadlock/livelock, etc) Does it mean, you need greater attention to detail? (mistakes that wouldn't matter become serious) Does it mean, you need greater working memory? (remembering what needs locks, and what already has locks; in addition to more ordinary side effects and possible exceptions etc) Does it mean, you need greater fluid intelligence? (reasoning about which locks can be safely composed, or which memory transactions will have too much contention)