walk the line

Short definition from Wiktionary

Verb

1. 1
   To maintain an intermediate position between contrasting choices, opinions, etc.
2. 2
   To act in a non-destructive or damaging manner, whether physically or mentally to those you hold dear and/or respect; to exercise self-control.
3. 3
   To mark or secure a boundary by walking along it.
4. 4
   To participate in the procession at a graduation ceremony; to graduate.