Is it difficult to become thechief of a secret service?

I think about people like Himmler or communists like Trotsky, Dzerzhinsky, Yagoda, you name it. They were not stupid people, that's for sure, but how did they know how to manage and coordinate such complex institutions without any previous experience in the police, secret service, government, etc.? They should have failed miserably, shouldn't they?