Definition & Meaning of "[step|be] out of line"

What is the origin of the idiom "step out of line" and when to use it?

The origin of the idiom "step out of line" can be traced back to military formations and drills. In formal military settings, soldiers are required to maintain precise alignment and positioning within the formation. Any deviation from the straight line or the assigned position is considered a breach of discipline and order. Stepping out of line disrupts the visual unity and uniformity of the formation, often resulting in reprimands or corrective actions. It is commonly used in personal, professional, and societal settings to address instances where someone's actions, conduct, or statements go against established boundaries.