A Justified Belief can fail to be true for at least 2 reasons: 1) because we lack the evidence or awareness of the evidence to justify the true belief, or 2) because we have chosen poor justifications, such as logical fallacies.
Logical fallacies are reasoning that have provably failed to determine the truth of a hypothesis or belief, and are therefore not useful for separating the wheat from the chaff. Example: "Well Socrates thought the sun revolved around the earth, and he was a smart guy." Fallacy: appeal to authority.
True Belief, while true, is indistinguishable from false belief if it is not justified. Just as many once thought the sun rotated around the earth and believed fire is hot, we can have true and false beliefs. We need justification to separate the wheat from chaff.
While Justified True Belief is currently the best understanding of how to arrive at correct conclusions, even a justified true belief can be wrong. Ever JTB we have should come with the humble understanding that it is only our "current best interpretation".
Those who have an accurate understanding of the world are more capable at navigating dangers and effecting change. Meteorologists who don't understand what temperatures cause rain to become snow are going to be less effective at their job than those who do.