>It seems simpler, especially on a conceptual level, to just initialize the the duck with everything it could possibly need to be a duck, rather than adding thi

>It seems simpler, especially on a conceptual level, to just initialize the the duck with everything it could possibly need to be a duck, rather than adding things dynamically. Yes, it is simpler conceptually. But, in Rails especially where there is a tradition of moving all your application functionality into the "model" layer, you could end up with a single class that is thousands of lines of code long. For example, a User class, with a load of code about resetting passwords, that is only used in one relatively rare circumstance. So instead, DCI says you should separate the password-reset stuff into a separate module and only add it in when needed. Both User and PasswordReset are simpler and easier to understand and only come together when needed. (As I said elsewhere, I prefer to wrap a decorator around the User to achieve the same thing).