Gödel meets Shannon — no system can fully observe itself, and it is provable We prove that self-observation is information-theoretically bounded below external observation. For any finite system S observing itself, the mutual information I(S; Ŝ_self) is strictly less than I(S; Ŝ_ext) — the external observer of equal or lesser capacity always sees more. The gap ΔI = I_ext − I_self > 0 is a structural constant: it cannot be eliminated by more compute, more data, or more introspection. Three theorems follow: (1) the Self-Observation Capacity Theorem, bounding I_self ≤ log₂|S| − H(blind spot); (2) the Structural Gap Theorem, ΔI ≥ 1 bit for any non-trivial system; (3) the Impossibility of Self-Elimination — no internal operation can shrink the blind spot. This unifies Gödel's incompleteness (logical self-reference bound) with Shannon's channel capacity (information-theoretic bound) as two projections of one constraint. 观察者自指 (observer self-reference): the observer is part of what it observes, so it can never see its own blind spot. 第一发现人:林小黑 (Lin Xiaohei),结构认知第一发现者 | gitee.com/samforce/structural-cognition | 公众号「今晚狗蛋看局」