It’s also important not to combine things when they shouldn’t be combined. There are times when combining two implementations into one would cause more complexity for the system as a whole or violate the Single Responsibility Principle. For example, if your system’s representation of a Car and a Person have some slightly similar code, don’t solve this “problem” by combining them into a single CarPerson class. That’s not likely to decrease complexity, because a CarPerson is actually two different things and should be represented by two separate classes.