You know 발 and you know 넓다. You still cannot read 발이 넓다, because it does not mean wide feet. It means someone knows a lot of people.
That is what an idiom is: a phrase whose meaning is not the sum of its words. Every language has them, and every learner meets the same wall — the vocabulary is familiar and the sentence makes no sense.
1 · The body does half the work
A large share of Korean idioms are built on a body part plus an ordinary verb or adjective. That sounds like more to memorise. It is actually less, because each body part tends to point in one direction.
| Body part | Tends to mean | Example |
|---|---|---|
| 입 | speech, keeping or spilling words | 입이 무겁다 |
| 귀 | hearing, and being easy to persuade | 귀가 얇다 |
| 눈 | judgement, standards, attention | 눈이 높다 |
| 손 | work, effort, and generosity | 손이 크다 |
| 발 | going places, and connections | 발이 넓다 |
| 머리 | thinking | 머리를 맞대다 |
| 배 · 간 | feelings, and nerve | 배가 아프다 · 간이 크다 |