I've been reading up on vector math here and here thinking about cross and dot products, and studying the unity vector3 documentation waiting for the right function to jump out and say "oi, use me!". All of which has been a whole lot of fail until I went and drew myself this diagram.
Probably makes no sense at all to anyone else, but total duh moment for me.
The lesson here? Remember I have a visual brain.
In other news, the Interwebs at our new house is connected today, woop woop!