My first job in Silicon Valley I had no idea I should be saying 'no' to unreasonable demands. I burned out pretty hard. Encouragingly, when I started saying '

My first job in Silicon Valley I had no idea I should be saying 'no' to unreasonable demands. I burned out pretty hard. Encouragingly, when I started saying 'no' I started getting taken seriously as an engineer. The conversation after 'no' includes real engineering topics on resources, schedules, techniques and backup plans. 'Ok, how do we get this done?', not 'You're fired'.