To expound on your last point: I agree that you have to be able to stop yourself from always getting drawn by curiosity into the rabbit-hole, but in my experien

To expound on your last point: I agree that you have to be able to stop yourself from always getting drawn by curiosity into the rabbit-hole, but in my experience one of the things that has separate the mediocre developers from the great ones is their ability to cross those layer boundaries. You don't have to know everything about every layer, but it helps to know enough about each one to have a general sense of how it works, and to know where to start digging if you do need to go deeper. Obviously this kind of experience takes time to build up. For example, if you are doing front-end JavaScript development it can be very good to understand HTTP, and have at least a vague idea of how things like TCP/IP and DNS work. Nothing kills productivity like hitting a bug that you can't even investigate without someone else's help.