Most engineers think Terraform immediately changes infrastructure.
It does not.
Terraform first reads the real environment, then compares that data against your configuration. Only after that comparison does Terraform decide whether to update, replace, or leave resources unchanged.
This process is why terraform plan exists. The plan is the calculated result of Terraform comparing desired state with actual state.
It is also how Terraform detects drift. If someone changes a resource in the console, Terraform will discover the difference during the next refresh and propose a correction.
Understanding this sequence explains many confusing Terraform behaviors. Unexpected replacements, drift detection, and plan output all come from the same engine.
Terraform is not a deployment tool.
Terraform is a reconciliation engine.