…（的）症结所在／问题所在
where the crux lies; the root of the problem
Structure
X 才是／正是 （问题的） 症结所在／问题所在
What it means
Names where the real trouble lies: 所在 is “the place where something lies”, so 症结所在 is the crux, the root of the problem.
How it is built
X + 才是／正是 +（问题的）症结所在／问题所在, or after 找到／指出／分析: 只有找到问题所在，才能对症下药 (Only by finding where the problem lies can you prescribe the right cure).
When to use it
Formal and analytical, at home in reports and commentary; it usually closes the sentence. Same frame: 关键所在 (the key), 希望所在 (where hope lies), 职责所在 (one's duty).
Watch out
No verb after it: ✗症结所在在于管理混乱 ✓症结在于管理混乱, or ✓管理混乱才是症结所在.
Examples
诸多问题积累了二十多年，青训薄弱和急功近利才是症结所在。
A great many problems have piled up over twenty years, and it is a weak youth system and the hunger for quick results that lie at the heart of them.
只有找到问题所在，才能对症下药。
Only by finding where the problem lies can you prescribe the right cure.
很多人以为是工资太低，其实管理混乱才是这家工厂的症结所在。
Many think the wages are too low, but the real crux of this factory’s trouble is chaotic management.
Learn this in Lesson 149 · HSK 7–9: 中国足球为什么难 (Why Chinese football struggles)
A dialogue, a reading, word cards with audio and a drill that uses it, in Learn Chinese with Bao. The first lessons of every level are free.
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