Hasty Generalization
The speaker cannot himself examine all the specific instances, he cannot consider all the illustrations which might support his position, but he must be careful of a too hasty generalization.
Having talked with a dozen returned soldiers he may not declare that all American army men are glad to be out of France, for had he investigated a little further he might have found an equal number who regret the return to this land. He must base his general statement on so many instances that his conclusion will convince not only him, but people disposed to oppose his view.
He must be better prepared to show the truth of his declaration than merely to dismiss an example which does not fit into his scheme by glibly asserting that "exceptions prove the rule." He must show that what seems to contradict him is in nature an exception and therefore has nothing at all to do with his rule. Beginning speakers are quite prone to this fault of too hasty generalization.