a fine line
US /ə faɪn laɪn/
UK /ə faɪn laɪn/

1.
une fine ligne, une distinction subtile
a subtle distinction or difference between two things that are very similar but can have very different consequences
:
•
There's a fine line between confidence and arrogance.
Il y a une fine ligne entre la confiance et l'arrogance.
•
It's a fine line between being helpful and being intrusive.
Il y a une fine ligne entre être serviable et être intrusif.