DRY and evolution
When you up to implement a feature similar to what you already have, there’s a huge temptation to refactor and abstract existing code right away. Sometimes you even have a perfect idea how it should be done.
Nevertheless, Don’t Do That.
Take an existing class, copy it, rename and update to meet your needs. Test, tweak, test again. You will see clearly how it is different from the original code. Don’t rush to extract common code, let yourself test/tweak more. Of course, don’t let it stay unDRY for a long time: it may become hard to refactor them later when you forget what you were actually doing.
In other words you should let your code evolve in a natural way like Darwin prescribed. Replicate and mutate the code: you will see better solution among the options. Then according to the Rule Of Survival Of The Fittest delete everything not worth living.
In many-many cases this technique helps to avoid wasting time on fitting code into wrong abstractions built on pure imagination.
[Blames himself for the mistakes of the past.]