You can think of penitent as a sore place inside someone who knows they did wrong. The soreness does not just sit there: it pushes the person to do something — to say it out loud, to pay it back, to walk somewhere and down. Every use of the word is a different distance along that push, from the feeling on a face to the person carrying it out in public.
From the word’s history
From Middle English, from Old French, from Latin paenitens (penitent), the present participle of paeniteo (to cause to repent; to regret, repent) — literally 'regretting', a feeling caught in the middle of happening.
經過中古英語、古法文，來自拉丁文 paenitēns，那是動詞 paeniteō（使人後悔、懊悔）的現在分詞，字面上是「正在後悔的」。現在分詞這個形式本身就帶著「進行中」的味道，跟這個字「心裡的痛還在推著人」的畫面正好吻合。
Wiktionary entries for penitent, adjective and noun (kaikki:3f6f69a190036ae4:527836777 and :527847478), supplied in this packet
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