walk the line

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb idiomatic To maintain an intermediate position between contrasting choices, opinions, etc.
• verb idiomatic To behave in an authorized or socially accepted manner, especially as prescribed by law or morality; to exercise self-control.
• verb To mark or secure a boundary by walking along it.
• verb idiomatic, US, education To participate in the procession at a graduation ceremony; to graduate.