倒進去的是時間和力氣
把「沒有剩下」從帳本搬到一段討論或一條研究路線上。這一步走得很自然，因為 profit 本來就不只指錢，也指任何得到的好處。
adjective · C1
Bringing no benefit, so that the time and effort put in lead nowhere. It is used about things like arguments, discussions and lines of research.
沒有助益的；白費工夫的
核心畫面
One way to hold this word: you put something in, you wait, and at the end nothing is left over. That leftover is what profit means, and un- ... -able says there is none to be had. When what you put in is money, the leftover is money, and the word is the plain business one: a shop, a route, an app that does not pay. When what you put in is time, effort or talk, the leftover is any kind of gain, and the word says the hour is gone and nobody is further forward. Same picture, different thing poured in.
可以想成：你投進去一些東西，等到最後，什麼都沒有剩下來。那個「剩下來的」就是 profit，而 un- 和 -abl…更多收起
可以想成：你投進去一些東西，等到最後，什麼都沒有剩下來。那個「剩下來的」就是 profit，而 un- 和 -able 合起來說的是：這裡沒有剩的可能。投進去的是錢，剩下的就是錢，這時它是商業上的常用字，講不賺錢的店、路線、app。投進去的是時間、力氣、談話，剩下的就是任何一種收穫，這時它說的是：時間花掉了，沒有人往前走一步。同一個畫面，只是倒進去的東西不一樣。From the word’s history
The word is un- plus profitable, which is built on profit; profit itself once meant gain of any kind, not only money, which is why the wider sense does not feel like a stretch.
這個字是 un- 加上 profitable，而 profitable 建在 profit 上面。profit 本來泛指「得到的好處」，不只是錢。所以「沒有收穫」那個用法並不是硬掰出來的，而是保留了這個字比較舊的範圍。
Wiktionary entry for unprofitable (kaikki extract, source_ref kaikki:3f6f69a190036ae4:1239711437): "From un- + profitable."
From the picture
Also in this word
adjective · B2
Making no money. An unprofitable business, shop or bus route takes in less than it costs to run, or at best only just covers its costs.
不賺錢的；無利可圖的