There is a small word hiding in the middle of this one: fill. To fulfil something is to fill it up to the line that was promised — the dream comes true, the person has enough, the order goes out of the door. Un- puts the cup back down still empty. That is the whole word: something was measured out and expected, and it has not arrived yet. What changes between the uses is only what was supposed to be poured in.
From the word’s history
The word is simply un- plus fulfilled. The un- goes back through Old English and Proto-Germanic to an old way of saying not, and it is the same un- you meet in unhappy and unknown.
這個字就是 un- 加上 fulfilled。un- 一路往前接到古英語和更早的日耳曼語，意思一直都是「不」。它和 unhappy、unknown 前面那個 un- 是同一個。
Wiktionary etymology tree supplied in packet (kaikki:3f6f69a190036ae4:1417816411): From un- + fulfilled; un- traced through Old English un- to Proto-Germanic *un-.
登入就可以看每一支怎麼連回核心畫面。