정신줄 꽉 잡아. 나사 꽉 쪼여.

There is an expression that says, 

나사가 풀린 것 같아 (NaSaGa Pullin Geo GaTda) 

정신줄 꽉 잡아 (JungShinJul KKwag Jab Ah) 

"I feel like a screw is loose, so hold on tight."

The head is a machine, and one of its accessories, the screw is a little loose, so when the machine is not working well, the screw comes loose. It's missing a screw. 

그는 약간 나사가 풀린 것 같아. He's a little loose. 

사실 그는 나사가 하나 빠진 것 같았어. Actually, he seemed to have a screw missing.

정신줄 (JungShinJu, mind string, String of thoughts) 

It is an expression that caricatures the human mind as a string, such as "letting go of your mind" or "letting your soul go." It is said that when you learn about neurons as a neural transmission circuit in middle and high school, it is connected by strings, so it does not feel strange to express it as a "string."

Meanwhile, there is a Korean proverb that says, "Even if you are bitten by a tiger, if you keep your mind, you will survive."

 '호랑이에게 물려 가도 정신만 차리면 산다'

The meaning of this proverb is that if you keep your mind, you can overcome any crisis.

A similar expression is,

'개념은 안드로메다로' 

"Concepts are to Andromeda" (It means that important concepts are far away in space.) 

So, when you are being lazy at a critical juncture, doing something that is far from important, or not finding the important point, you use the expression 정신줄 꽉 잡아 (JungShinJul KKwag Jab Ah), 나사 꽉 쪼여. (NaSa KWack Jjo Yeo)