little knowledge is a dangerous thing

a little knowledge is a dangerous thing

proverb Having a precursory or limited amount of knowledge about something can make one overestimate how well they will be able to do something much larger in scope or scale. Just because she painted her room by herself, now she thinks she can do the entire house—inside and out! A little knowledge is a dangerous thing, I tell you.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

little knowledge is a dangerous thing

 and little learning is a dangerous thing
Prov. 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.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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References in periodicals archive ?
HAVING read the letter (June 9) written by Jon Haddy, who is also the secretary of the Llangollen Plaid Cymru branch, I was reminded of the old adage "a little knowledge is a dangerous thing".
While this transformation has generally been lauded in postindustrial societies like Great Britain and the United States, it has left many people - and countries - out in the cold, Neef suggests in A Little Knowledge Is a Dangerous Thing.
Source: A Little Knowledge Is a Dangerous Thing: Understanding Our Global Knowledge Economy by Dale Neef.