All methods are equally valid. You believe your mother's warning. The validity of this type of learning, faith, is dependent upon the object of faith. In this case, the object is your mother and her veracity. You may also use empiricism to determine whether it is hot.
Empiricism is the scientific method and utilizes the senses.
Good way to learn, a little painful, but effective. The third method, rationalization, involves reason. You can reason that there is steam coming from the pot on the stove and that things like your soup when they come off the stove are hot, therefore, the stove must be hot. This method utilizes the ability to think, the quality of your mind. Each of these methods is valid.