This just means that you already have an idea of what kind of object should go where, you just never wrote it down. And because you never wrote it down it becom

This just means that you already have an idea of what kind of object should go where, you just never wrote it down. And because you never wrote it down it becomes hard to generalise things when you eventually want to reuse some method, since you never made explicit which operations an object should support to be able to reuse that method. Also you have no guarantee that what you think the types should be is actually consistent.