Fundamental attribution error
Sometimes as testers it can be easier to explain issues away, rather than address them. One such bias that often comes into play when this occurs is the fundamental attribution error. This is where we attribute events or behaviors to external factors ("the task, other people, fate") or internal factors ("ability, mood, effort") in an effort to explain something away and make it irrelevant. Found a bug but in the "wrong" environment? Think there might be a security issue, but don't think you're "qualified" to look for security problems? An extension of this can be attributing your own behavior to situational factors, but attributing others’ behaviors to personal factors. For example, "If I miss that bug it’s because the system is so complex that no one could ever find it except by luck, but if Jimmy misses that bug it’s because he’s incompetent."