If you are writing a story, miracles or abnormal events may be bad art, or they may not. If, for example, you are writing an ordinary realistic novel and have got your characters into a hopeless muddle, it would be quite intolerable if you suddenly cut the knot and secured a happy ending by having a fortune left to the hero from an unexpected quarter. On the other hand there is nothing against taking as your subject from the outset the adventures of a man who inherits an unexpected fortune. The unusual event is perfectly permissible if it is what you are really writing : it is an artistic crime if you simply drag it in by the heels to get yourself out of a hole.