The phrase "being mistaken" can be replaced with various synonyms depending on the context. For example, "misunderstanding," "misconceiving," "misinterpreting," "erroneously believing," "confusing," "misjudging," or "misreading" can be used in its place. These words all refer to the act of being wrong or inaccurate in one's perception or judgement of a situation. Using synonyms can help add variety to one's writing and avoid repetition, while also conveying a more specific meaning or tone. It is important to choose the appropriate synonym based on the intended message and audience, as some may be more formal or informal than others.