there is a fine line between

there is a fine line between (something) and (something else)

There is a very narrow or indistinct division between two deceptively similar things, one of which is worse than the other. As a new parent, you learn that there's a fine line between looking out for your child's welfare and being overprotective. A: "I only borrowed your sweater, I swear!" B: "Well, there's a fine line between borrowing and stealing, isn't there?"

See also: and, between, fine, line, there

there is a fine line between (something and something else)

There is little difference between something and something else. There is a fine line between a frown and a grimace.