It's easy to reach agreement alone.
Maybe you're working on a project independently and you're the only stakeholder and user.
More likely, you're working with other people to serve other people. In that scenario, making maps and diagrams alone at your desk is not practicing information architecture.
Your whole team should be able to influence and react to your tools and methods. You should be making prototypes to get feedback from users on language and structure.
Getting everyone involved early is crucial. Every step you take should come from the direction you choose together. If you don't get agreement up front, prepare for more work later.
When you see the world through the eyes of other people, you can spot weaknesses and opportunities for improvement. Don't hide from other stakeholders or wait until the end of the project to talk to users.