YAGNI. Believe it.
One way to avoid introducing problems in your codebase is to avoid adding unnecessary extra bits. When you add these things to your code, you are wasting time that you could better spend supporting the actual requirements. There is only so much time in the day. In a rush to finish features in time to meet deadlines, the quality of the desired product will suffer if you spend time on items that aren’t required.
When a developer adds extra features that are not part of the requirements, this results in a lot of extraneous code. You may end up adding unneeded classes, methods, logic structures, and database elements. These, in turn, will need additional tests and examples. If a certain percentage of code has bugs, on average, then it follows that more code means more bugs.
All of this extra code and time spent on unasked-for requirements will likely delay the release of the critical features that your sponsor desires. These delays result in reduced revenues for the business, which everyone wants to avoid. You don’t want to be known as the person who regularly causes delays.
Stick to the requirements, and you’ll have fewer problems and waste less time. Write the tests to meet all of the business requirements. Write the code that satisfies the tests. Then stop.