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

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
Farlex Dictionary of Idioms.

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.
See also: between, fine, line, there
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • there is a fine line between
  • a fine line
  • a fine line between something
  • a thin line
  • give (one) a line
  • give a line
  • curse (someone or something) under (one's) breath
  • ring a bell
  • slur over
  • slur over (something)