I would make a big distinction between 'without knowing' and "without worrying about." Software productivity is directly proportional to the amount of the system you can ignore while you are writing the code at hand. But not knowing how stuff works makes you less of an engineer and more of a artist. Cause and effect and reason are key tools, and not knowing about TCP handshake or windows just makes it difficult to figure out how to answer fundamental questions about how your code works. It means things will be forever mysterious to you, or interesting in the sense of biology where you gather a lot of data rather than mathematics where pure thought can give you immense power.