How was work on the original iPhone? That is precisely what one of the engineers of Apple who took part in the so-called ‘Project Purple’, an ultra-secret project in which it was only possible to work if one accepted not only endless days, but also an environment in which the Secrecy was absolute.
So much so that as detailed this engineer, named Terry Lambert, had to sign a confidentiality agreement (NDA) not to ensure that he was not going to tell anything about that project: he signed it to know the name of the key project. That was only the first measures of security obsessional who managed to protect that secret until the end.