It is not right to make a promise unless one is sure he can fulfill the promise.
This sentence contains one main and two subordinate clauses.
The main clause is <em>It is not right to make a promise, </em>and the two subordinate clauses are <em>unless one is sure </em>and <em>he can fulfill the promise.</em>
You take a story and explain the entire thing with only a couple paragraphs, and you don't want to give away any special details that way a person can know a little about the book and want to read it. Like a "A dog and His Ball" is about a lost dog who doesn't have a family and finds an old ball to play with. You would put this on the back of a book and then people would be drawn to read this book. ( I just made something up so it may not make sense sorry.)
I'm not really sure I understand what you are asking, but I tried to answer the best I could, please let me know if this isn't what you meant.
is bad for your health and
