generalize from (something)
To reach a conclusion about someone or something despite a lack of supporting evidence or information. I know you don't like Rosemary, but I think you're just generalizing from your limited interactions with her—I've always known her to be a very sweet woman.
generalize from something
to assume a general pattern in something from specific observances of something. You can hardly generalize from only two instances. You can't generalize anything from the testimony of a single witness!