1.
not straightforward; not easy to deal with; tricky
Describes a person, situation, or problem that cannot be handled with ordinary methods and requires extra effort or skill.
An idiomatic expression meaning that ordinary approaches won't work. Literally, 一筋縄 means "a single rope" — the image is that a single rope (simple method) isn't enough to restrain or control someone or something.
Usage
Almost always used in the negative form ではいかない or じゃいかない. Can describe people (stubborn, clever, difficult), problems (complex), or situations (unpredictable).