In Chinese, the “好不X” (haobu X) structure expresses three types of meanings (negation, affirmation, and both affirmation-negation), where X exhibits differences in semantic symmetry. So far, no systematic explanatory theory has been proposed to account for these differences. Therefore, this paper presents and argues for an explanatory hypothesis that progresses through four stages: “很不X” (henbu X) => “好不X” (haobu X) (negation) => [ironic use] “好不X” (haobu X) (affirmation) => expansion and obstruction of affirmative “好不” (haobu). Specifically, (1) the basis of the negation “好不X” (haobu X) is attributed to “很不X” (henbu X), and the semantic asymmetry of X (excluding negative words) is explained using politeness principles, irony, and the semantic valence of negation results; (2) the ironic use of the negation “好不X” (haobu X) gives rise to the affirmation “好不X” (haobu X); (3) the grammaticalization and expansion of the positive meaning of “好不” (haobu) extend to X, which cannot appear in the negative meaning “好不__” structure (including words with opposite meanings and high polarity positive words). This explains the semantic symmetry of X in the positive meaning “好不X” (haobu X) structure; (4) when the affirmation “好不” (haobu) expands to the negation “好不X” (haobu X), it encounters both obstacles (X includes neutral and some positive words) and compatibility (X is some other positive words), thus explaining the semantic asymmetry of X in the affirmation-negation “好不X” (haobu X) (i.e., X is positive words).