A Japanese manager, describing a team member before a difficult conversation: "彼、ちょっとナイーブだから…"
You hear: he's a bit of an idiot, be careful what you sell him.
He means: he's sensitive, be gentle with him.
You then run the meeting completely wrong, with total confidence.
The English "naive" comes with a whiff of contempt: inexperienced, easily fooled. The Japanese ナイーブ arrived through a different door and kept the French flavour of the word — unspoiled, delicate, thin-skinned — and it is broadly affectionate.
It is used about people who take things to heart, and also about skin (ナイーブ肌 is sensitive skin — there is a soap brand called Naive, which no English speaker can look at without pausing).
Japanese has plenty of native words for genuinely gullible — 世間知らず, お人好し, 単純 — so the borrowed word was free to take a different, softer job. That is usually why a loan word survives: the language had a gap in a very specific spot.
English fused two ideas into one word and made both of them insults: sensitive and foolish. Japanese separated them and kept only the tender one. Look at what that means in practice — in English you cannot describe someone as emotionally delicate without slightly mocking them. Japanese can. That is a real difference in what each language lets you say kindly.