Most automation projects do not fail loudly. They produce a suite, the suite goes green, and then over six months it becomes slower, less trusted and more expensive to maintain than the manual process it replaced — until someone quietly adds a step to the release checklist that says "re-run if red".
That failure has a shape, and it is almost always structural rather than a matter of effort or tooling. This guide sets out the decisions that determine whether a suite compounds or decays: what to automate first, which level to write each check at, how test data is owned, and what has to be true before automation returns more time than it consumes.
A red build nobody believes is worse than no build at all. It teaches a team to ignore the one signal they were paying for.