However, "one and only one" adds emphasis to the fact that there is only one, and draws attention to it. For example, the student who is the only one who failed, might feel more ashamed if the teacher uses "one and only one", as the teacher might be perceived as purposely drawing attention to that fact, for whatever reason.
Some people say a dog=one, dogs=ones, the dog=the one=that, and the dogs=the ones=those. It's a rule of thumb, but what I found was that this is not always correct.
What is the proper way to use "ones" or "one's" this word in sentence?