One of the numerous mitzvos bein adom l'chaveiro mentioned in this week's parsha is the prohibition of believing lashon hara:The Torah commands us, "Do not accept a futile report" (Shemos 23, 1). Rashi cites the translation of the Targum, "Do not believe a false report," and explains that this mitzvah includes two separate warnings. Firstly, it is forbidden to accept lashon hara. Additionally, a judge is warned not to listen to one party when the other party is not present.
Interestingly enough, the commandment not to accept a false report is not referring to believing lies. Rather, it refers to believing lashon hara which is for the most part a true account. (If it would not be true it would fall under the category of "motzie sheim rah"). What is false about lashon hara? Rav Wolbe (Shiurei Chumash) explains that truth is not measured by the words spoken; it is measured by the intent behind them. Even a perfectly true statement, when said with the intention of causing another harm, is considered false. It is this intention to harm another person which is inherently false.
This idea is found in Maseches Sukka (32b) where the Gemara attempts to identify the hadassim referred to by the Torah. The Gemara eliminates a certain poisonous plant because it does not conform to the Torah's principle, "Love truth and peace" (Zecharya 8, 19). Though a poisonous plant certainly does not fit under the title of "peace," why does the Gemara also consider it a lack of truth? The answer is that an object which harms is considered "false."
The converse is also true. A blatantly false statement is considered true when the intention is good, and the situation warrants such words. We know that Hashem is the G-d of truth, and nevertheless, when repeating to Avraham what Sarah had said about him, He changed the wording so that Avraham would not be offended. The intention was pure and thus the statement was true.
This is the rationale for the second prohibition included in the above pasuk. The attempt to tell one's version of the story first, does not mean that his account is false. Yet, since his intention is to cause the judge to have a bias toward his version of the story, thereby harming his opponent, his words are labeled as false.
Sheker is the only middah that the Torah warns us to stay far away from (ibid. 23, 7). Rav Wolbe notes that regarding forbidden relations the Torah states, "Do not come close" (Vayikra 18, 6), while regarding sheker we are told, "Distance yourself from a false word." We must bear in mind that it is not merely false words from which we must run, but also true words said with a negative or harmful intention. "But it is true" is not an excuse for a harmful word, because in reality there is no greater falsehood than that!