竟自 is a literary adverb meaning 'actually', 'unexpectedly', or 'to one’s surprise'. It conveys a sense of contrast between expectation and reality — often highlighting that something happened contrary to what was assumed, anticipated, or deemed likely. The character 竟 (jìng) means 'after all', 'in the end', or 'unexpectedly', while 自 (zì) adds emphasis on spontaneity or unmediated occurrence — together they intensify the nuance of unplanned, almost defiant realization.

This term is common in formal writing, classical-influenced prose, and literary dialogue. It frequently appears with verbs indicating action or change (e.g., 走开, 离开, 说出, 决定), especially when the subject acts independently or contrary to social expectation. Though grammatically similar to 竟然, 竟自 carries a stronger implication of autonomous, unassisted action — the 'self' in 自 underscores agency. It is rarely used in casual speech and is more frequent in written narratives expressing emotional tension or irony.