One way to hold this word is a line of people who were counted in before anyone asked them. Staying put takes no effort at all; leaving takes one deliberate step out of the line. An opt-out is that step, or the gap in the rope that lets you take it. Every use keeps the same two parts: something that would include you by default, and a decision to stand outside it.
可以想成一排人，而且他們是在還沒被問過之前就先被算進去的。留在隊伍裡完全不用花力氣；要離開，才得自己往外跨那一步。opt-out 就是那一步，或是繩子上讓你跨出去的那個缺口。它的每個用法都留著同樣的兩個部分：一個預設會把你算進去的東西，加上一個「我不要」的決定。
From the word’s history
Wiktionary records the word as formed from opt plus out. The verb opt is simply to choose, and out sets the direction of the choice, so the noun names a choice that points away from the group.
Wiktionary 記載這個字由 opt 加 out 組成。動詞 opt 就是「做選擇」，out 則決定了選擇的方向。所以這個名詞講的是一個「往外」的選擇——選了它，人就站到團體外面。
Wiktionary, "opt-out"
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