I disagree. If you will really need it, then just make it a library. This is not 1960 when we were still figuring out software. You are not writing something new anymore, the problem has been solved enough time that you can look around and figure out what will really be needed in other projects and what will not. This is something your architects should be doing as getting it right is important and you will regret not doing so (when you have 10 different implementations of the same thing all slightly different)

Now I will agree that developers are often wrong. We often think something we write is important than it really is and so make it reusable when it never will be. We often think something won't be reused when it really would be. This is a hard problem, but that doesn't mean you should not think about it and work hard to get things right.