Followings things may be go wrong in test automation:
Ignoring automation, while planning the development phases.
In design Phase not choosing the right technology.
In coding Phase not automating the right test cases.
Tool selection might go wrong.
Test script not be updated when application is continuously changing.
Test data should be unique, if the same data is available on the application then the application will not accept the data that we are going to add via automation.
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