悟

Vertical heart radical on the left — the side-form of 心. Anchors 悟 in the mental-state family alongside 想, 忆, 怕, 怀. Carries the meaning core: comprehension and realisation are inner events of the heart-mind in classical Chinese psychology, not abstract intellectual operations divorced from feeling.

Right component supplies the sound: 吾 wú → wù with tone shift. Adds a sharp semantic flavour: 吾 is the literary first-person pronoun, so 忄 + 吾 reads as 'the I-mind,' the moment when self-awareness dawns — a perfect picture of realisation. 悟空 (Sun Wukong, 'awakened to emptiness') uses exactly this sense.