Depicts rope wrapped around two pieces of wood to keep them straight. Based on the original meaning "straighten". The current meaning is a phonetic loan.
Shuowen Jiezi
《說文》：“弗，撟也。从丿，从，从韋省。”
Original meaning
straighten
Components
◎(iconic) — Depicts two pieces of wood.
◎(iconic) — Depicts a rope binding the pieces of wood together to keep them straight.