 Why was Humphrey being observed?
What made it possible was Humphrey Fownes' abstraction; he was an uncommonly preoccupied individual. It all went off very smoothly, like a game of put and take—the sole difference being that Humphrey Fownes had no idea he was playing. Humphrey Fownes strode through the puffs of falling glass still intrigued by a temperature that was always 59 degrees, by a humidity that was always 47%, by weather that was always Optimum. It was this rather than skill that enabled the police to maintain such a tight surveillance on him, a surveillance that went to the extent of getting his fingerprints off the postman's bag, and which photographed, X-rayed and chemically analyzed the contents of his pockets before returning them.
 he didn't act like he was expected to
 he didn't act like he was expected to  to make sure he wasn't a danger to society  he was to be observed before he was allowed to be married  he was suspected of committing crimes