Solid lines, dotted lines, and accountability
Org charts use visual conventions to show authority and information flow. A solid line shows direct reporting: this person is your manager, you attend their one-on-ones, they evaluate your performance and control your compensation. A dotted line shows a secondary reporting relationship: you work for this person on their project but your primary manager is someone else. A dashed line sometimes indicates influence or consultation without formal reporting.
The critical principle is that every person has exactly one solid line manager. When a person has dual solid-line reporting (two managers with equal authority), accountability disappears. They can play managers against each other. They have conflicting priorities and no clear way to resolve them. Dotted lines are fine; dual solid lines are dysfunction waiting to happen. Even the biggest matrix organizations respect this rule: primary reporting is solid, secondary is dotted.
Unclear lines and the politics that follow
Organizations that are vague about reporting relationships create politics. A person might report to Manager A but work on Manager B's team. Is Manager B their real manager? Does Manager A control their compensation? These ambiguities are where turf wars start. Manager A thinks the person should be promoted because they do good work; Manager B thinks they are not senior enough because they have not done work on B's priorities. No one is actually accountable for the person's career.
Clear reporting lines, even when lines are matrix-heavy, prevent this. A dotted-line relationship is honest: you work on this team, but this manager is your primary. It eliminates the pretense of equality and creates clarity about who has final authority. Organizations where reporting lines are explicit and communicated move faster because people know exactly who to escalate to, who controls their career, and where the buck stops.