expression
in short; in the end; after all
Used to summarize or boil down a situation to its essence, often when stating a conclusion or the fundamental point. Literally means 'when you boil it down'.
煎じ詰めると、彼の言いたいことは「努力が大切」ということだ。
In short, what he wants to say is that effort is important.
いろいろ理由はあるが、煎じ詰めるとお金の問題だ。
There are various reasons, but in the end it's a matter of money.
つまり is a more common and neutral way to say 'in short' or 'that is to say'. 煎じ詰めると carries a nuance of boiling down complex details to the core point.
要するに also means 'in short' or 'the point is', but is slightly more formal. 煎じ詰めると is more vivid and colloquial.
From the verb 煎じ詰める (to boil down, to condense by boiling) in its conditional form, literally 'when you boil it down'. Used metaphorically to mean getting to the essence of a matter.