It is important to know oneself.
Humble first-person pronoun used mainly by men in formal or self-deprecating contexts; can sound old-fashioned or stiff.
己が未熟なばかりに、ご迷惑をおかけしました。
It was due to my own inexperience that I caused you trouble.
Derogatory second-person pronoun used to address someone with contempt or anger; often heard in confrontational or rough speech.
己、よくも騙したな！
You bastard, how dare you deceive me!
Adverbial use meaning 'by oneself' or 'of its own accord'; often appears in set phrases like 己から (of one's own will).
彼は己から進んでその仕事を引き受けた。
He took on that task of his own accord.
俺 is a casual, assertive way men say 'I', while 己 used for 'I' is humble and formal, often sounding old-fashioned or self-deprecating.
お前 is a common, sometimes rude way to say 'you', while 己 used for 'you' is more explicitly derogatory and confrontational.
おのれ can mean 'oneself' but is also used as a contemptuous 'you', much like 汝, though おのれ is more often heard in modern dramatic speech.
己 is an old-fashioned, literary reflexive pronoun with a stern or self-reproaching tone, while 自分自身 is neutral and common in everyday speech.
all by itself; naturally; spontaneously; all by oneself
Standard kanji spelling; high-frequency in news and common usage.
Rare kanji spelling with okurigana; mostly seen in older or literary texts.
Derived from Old Japanese おの (self) + れ (nominalizer/suffix). The exact historical development is uncertain, but it has been used as a reflexive and personal pronoun since ancient times.