One way to hold this word: someone walks toward you carrying help — a review, a compliment, a service, a page of your poems — and what they set down leaves you worse off than before they came. The shape of a service is all there. The direction is reversed. That reversal is what dis- is doing, and it is why the word so often turns up where the harm was not intended.
From the word’s history
The packet's source entry derives disservice from dis- plus service. The prefix reverses the word it joins, so the modern meaning sits exactly where the parts point: the shape of a service, with the result turned the other way.
來源資料說 disservice 由 dis- 加上 service 構成。dis- 把後面的字反過來，所以今天的意思正好落在字面指的位置：形式上是服務，結果卻是反過來的。
Wiktionary entry for disservice supplied in evidence packet (kaikki:3f6f69a190036ae4:1362797901), etymology tree dis- + service
登入就可以看每一支怎麼連回核心畫面。