In the fifth perek (Avot 5:9) we learn that one of seven signs that distinguishes a chacham -- a wise person -- from a golem is that he or she does not deny the truth but concedes it. In other words, once you are shown to be wrong, don't cling on to your error but relinquish it and accept the truth.
That's not all. the process of setting oneself up on the basis of truth is listed (Avot 6:6) as one of the 48 items through which one acquires the Torah, and the mishnah even goes so far as to say (Avot 1:17) that truth, along with justice and peace, is one of the three foundational qualities that keeps the world going.
The truth can be elusive, frustrating and annoyingly inconvenient. Pirkei Avot pulls no punches when it comes to advocating the need to live by it -- even truth has its limitations when it comes into conflict with peace. But's a subject for another post.