醫療上的特效藥
子彈的目標是疾病，這是這個詞最早的用法。
noun · B2
A drug or treatment that cures an illness quickly and easily, without much effort and without causing other problems.
特效藥
核心畫面
One bullet that finds the target by itself. It ignores everything else in its way, hits the one thing that is wrong, and the whole trouble is over in a second. That promise — perfect aim, no side damage, no waiting — is what the phrase carries wherever it goes. It is also why people so often use it to say that no such thing exists.
可以想成一顆自己會找目標的子彈：沿路的東西它都不碰，只打中那個出問題的地方，一瞬間麻煩就結束了。這個承諾——百發百中…更多收起
可以想成一顆自己會找目標的子彈：沿路的東西它都不碰，只打中那個出問題的地方，一瞬間麻煩就結束了。這個承諾——百發百中、不傷別處、不用等——不管用在哪裡都跟著這個詞走。也正因為承諾太漂亮，大家最常拿它來說「其實沒有這種東西」。From the word’s history
Wiktionary records the phrase as a calque of German Zauberkugel, coined by the physician Paul Ehrlich as an allusion to the opera Der Freischütz, in which the magic bullets never miss. That never-missing bullet is exactly the picture the English phrase still carries.
來源記載這個說法是德文 Zauberkugel 的直譯，由醫師 Paul Ehrlich 造出來，典故來自歌劇《魔彈射手》(Der Freischütz) 裡百發百中的魔彈。那顆不會失手的子彈，就是今天英文裡還在用的畫面。
Wiktionary entry for magic bullet (kaikki:3f6f69a190036ae4:1339010316:4545): calque of German Zauberkugel, coined by Paul Ehrlich as an allusion to Der Freischütz; compare silver bullet.
Two branches
一招解決難題的辦法
同一顆子彈，只是目標從疾病換成任何難題。
noun · B2
One simple action or answer that is supposed to solve a hard problem all at once. It is used most often in the negative, to say that no such easy answer exists.
萬靈丹；一招解決的辦法