What causes an Argo CD application to remain OutOfSync after a sync operation?

An Argo CD application should transition to Synced after a successful sync, but it can stay OutOfSync when the manifest path or revision is incorrect, the destination cluster is unreachable, the argocd-manager service account lacks necessary RBAC permissions, or repository credentials are invalid. Diagnosing the issue requires inspecting sync logs and verifying each of these factors without altering the live configuration prematurely.

How can one verify that the destination server URL is reachable from the Argo CD instance? Which specific RBAC permissions are required for the argocd-manager service account to manage resources in the target namespace? What steps confirm that repository credentials or SSH keys are correctly configured and valid?