Ingenuousness is when a person is simple, trusting, and honest — not because they chose to be 'good', but because they have not had much life yet, so they have not learned to hide their thoughts or to expect other people to hide theirs. An ingenuous person says what they think. They believe you. They have not built the small walls that older people often put up. Though actually, this is not the same as being slow or foolish. You can be bright and still ingenuous: you just have not learned the game. The word is rather formal and a little old. Teachers and books use it more than friends talking. And here is the messy bit: it sits next to ingenuity on the page, but they are not a pair. Ingenuity is clever ideas and fixing things. Ingenuousness is openness. Mix them up and the whole meaning flips.

天真、純真（還沒學會防備的那種誠實）。勿與 ingenuity（機智、巧思）搞混。