I walk with everyone I speak to no one I knock at no door I am always certain What am I

I am to live, to breathe and to fight. With logic and rational, I can give light. For sense, for purpose, an argument, true. If nothing at all, then just to do.

Silent communicator of choices, guiding paths in unseen corridors, whispers clarity amidst the noise.

What is the one thing missing from the answer forty two?

I see all around, though that’s not my task, I sit on a wrist for convenience, you ask. I give you a detail tied to this place, one AU away shifts my measured pace.