How to identify “over engineering”

This is how I identify “over engineering”:

When adding complexity to code in order to…

• Cater for scenarios that will probably never happen. Eg. Switching to a different database.
• Optimize for performance where performance is not really critical.
• Make code super DRY, but as a result making code more difficult to follow/debug.
• Decouple code to such a degree that you can’t figure out how code will execute without attaching a debugger to see.

Secondly, what are the exceptions? When is adding complexity to code NOT over engineering?

• When it makes code more flexible (some complexity within reason is ok).
• When it makes code more testable.
• When it sets you up for success (eg. Making it harder to do “bad” things)