[Source:] Note that the substitute of “beside” for “outside” was perfectly appropriate since, at that time (although today obsolete), “outside” was one of the well-used meanings of “beside,” having first been recorded in the English Wycliffte Sermons in the 1370s.
[OED:] beside = †4. Outside of, out of, away from. Obs.
The prefix be- doesn't appear to mean 'out(side)'. So please expose and explain any (hidden and missing) semantic drifts and links. How did 'beside' evolve to mean 'outside'? What is a right way of interpreting the etymology, to understand how the semantic jumps abstracted and severed from the original literal meaning? What bridges the jumps with the original meaning?
The etymology of 'beside oneself' confused me: If your soul leaves your body, then yes, your departed soul is now outside of you. But it's unclear to me whether the soul is still beside you, or by your side. Maybe your soul aspired to the heavens and is nowhere near you anymore.
So how far out did beside mean?