嘴巴吞不下去
最字面的一支：拒絕的是真的食物。
adjective · C1
Unpalatable food or drink tastes unpleasant, so people do not want to eat it or cannot finish it.
難吃的、難以下嚥的
核心畫面
Picture a lifted to the mouth, and then the mouth refusing it. The tongue and the roof of the mouth say no, the head turns a little, and the spoon comes back down. That moment of not being able to swallow is the whole word. Sometimes what is on the spoon is real food. Sometimes it is a fact somebody is trying to make you take, and the refusal feels exactly the same.
可以想成一匙東西送到嘴邊，然後嘴巴拒絕了。舌頭和上顎說不要，頭稍微一偏，湯匙又放了下來。整個字就停在那個吞不下去的瞬…更多收起
可以想成一匙東西送到嘴邊，然後嘴巴拒絕了。舌頭和上顎說不要，頭稍微一偏，湯匙又放了下來。整個字就停在那個吞不下去的瞬間。有時候匙子上的是真的食物。有時候是別人要你接受的一個事實，而那種拒絕的感覺一模一樣。From the word’s history
Our Wiktionary evidence builds the word from un-, plus palate, which comes through Old French palat from Latin palatum, the roof of the mouth, plus the ending -able. So it literally says 'cannot be taken by the mouth', and the modern figurative use is that same refusal moved from food to facts.
手上的 Wiktionary 資料把這個字拆成三塊：un-（不）、palate（上顎、味覺，經古法語 palat 來自拉丁文 palātum）、-able（可以…的）。所以它字面上就是「嘴巴收不下的」。今天的比喻用法，可以想成同一個拒絕的動作，從食物換到了事實上。
Wiktionary via supplied kaikki extract 3f6f69a190036ae4, entry 'unpalatable' (adj), etymology_text (etymology tree: un- + palate < Latin palatum + -able)
Two branches
心裡吞不下去
同一個拒絕的動作，換成事實被推到面前。
adjective · C1
An unpalatable fact, truth, idea or choice is unpleasant and hard for people to accept, even when they know it is true or necessary.
難以接受的