Most Terraform failures are not caused by syntax.
They are caused by unclear module behavior.
A module is not just code.
It is a contract.
Inputs define what a caller must decide.
Outputs define what a module guarantees.
Assumptions define what Terraform cannot validate.
When these are undocumented, users guess.
Guessing creates incorrect infrastructure.
This lesson breaks down how documentation prevents misuse, reduces debugging time, and enforces stable module boundaries.
If your modules require reading the source code to understand behavior, the documentation has already failed.