Despite how it might look on Law & Order, trial lawyers don’t just impeach witnesses for the entertainment value.

“We impeach to show that an adverse witness is unworthy of belief … to show that their testimony is not credible, that you should probably not give a lot of weight to it, or because there’s some other reason that we don’t want the jury to rely on the testimony,” says Dennericka Brooks, the managing director of Legal Aid Chicago.