The cost to add it is often much higher, once the code has high fan in (lots of code paths depend on it). I am definitely a fan of not over engineering, but I'

The cost to add it is often much higher, once the code has high fan in (lots of code paths depend on it). I am definitely a fan of not over engineering, but I'm more of a fan of thinking. Think about your problem and your use cases, and about your own ability to predict the future. If you can predict future changes with high probability, then go ahead and design for those. If you're not a domain expert, you probably can't predict the future at all (and you probably grossly underestimate how bad your predictions are), so you should stick to the bare minimum.