Picture someone standing in a corridor full of doors, watching to see which one swings open. The moment one does, they walk through it. What makes them an opportunist is not their speed but the question they ask. They do not ask whether it is right, or whether they planned for it. They ask only whether it is open right now. Both uses of the word grow from that one habit: the person who changes their promises to fit the moment, and the person who takes the bike because it happened to be unlocked.
From the word’s history
Recorded as a borrowing of French opportuniste, from opportune plus the ending -ist: the person whose speciality is the right moment.
依據來源，這個字借自法文 opportuniste，由 opportune（時機剛好）加上 -ist（某種人）構成。字面就是「專做『時機剛好』這件事的人」，正好對上今天兩個用法裡共有的畫面。
Wiktionary entry supplied in this packet (source_ref kaikki:3f6f69a190036ae4:823902389:17017): 'From French opportuniste, equivalent to opportune + -ist.'
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