Pictograph of a nose viewed from the front — the bridge, the nostrils, the rounded tip. Chinese speakers traditionally point to their own nose (not chest) when saying 'me,' so the nose pictograph naturally extended to mean 'self.' The original 'nose' meaning was later rewritten as
鼻, freeing
自 to specialize in 'self, from, since.' Self-radical (Kangxi #132) — atomic, not decomposed further.