They may even tell plausible lies. We know these processes well. Many family arguments are adversarial. The defence is as determined to prove innocence. Neither of them could be said to be interested in telling the whole truth, even if they have taken an oath to do so.
Adversarial processes are competitive.
There are winners and losers, usually more losers than winners. Our economy is competitive. Much of our education system is competitive. So are most of our sports, and many other activities. There is also a variety of adversarial process which is sometimes called compromise.