a fine line

US /ə faɪn laɪn/
UK /ə faɪn laɪn/
"a fine line" picture
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.