a fine line

a fine/thin line

if there is a fine line between one thing and another, they are very similar although the second thing is bad (often + between ) There's a thin line between courage and foolishness.
See also: fine, line
References in classic literature ?
That's a fine line," he said at last, indicating with his thumb what pleased him.
A WORD OF CAUTION There's a fine line between being a reliable, in-charge chica and being an overbearing, bossy control freak[
Andrew Lorraine knows there is a fine line between Triple-A and the big-leagues.
That's a fine line to walk, between confidence and overconfidence, between feeling you're invincible and actually thinking you are.
But there's a fine line between challenging them and putting them in over their heads.
In the fourth annual Daily News Top 10/Bottom Five rankings for the call of the wild, we try to separate the Walk of Fame candidates from the Fame-impaired guys who walk a fine line between dumb and dumber: