Slang: Use your head

Definition: To think something through; to be rational and calm.


Example:
1) Use your head, Jim. You have to pass physics if you want to get your degree.


2) Tim never uses his head -- it's no wonder that he keeps getting into so much trouble.


Etymology: Your 'head' is where your brain is, so when you 'use your head', you use your brain to think.




fonte: www.peakenglish.com