little knowledge is a dangerous thing
and little learning is a dangerous thingProv. Cliché If you only know a little about something, you may feel you are qualified to make judgments when, in fact, you are not. After Bill read one book on the history of Venezuela, he felt he was an authority on the subject, but he wound up looking like a fool in discussions with people who knew a lot more about it than he did. A little learning is a dangerous thing.