There are plenty of synonyms to describe the phrase "failed to notice" that can be used to convey the same meaning or tone of a situation. A few of the options might include overlooked, disregarded, missed, neglected, skipped, and underestimated. Some others that could be used more situationally are disregarded, dismissed, ignored, misunderstood, didn't pick up on, or failed to recognize. Each of these synonyms can provide more depth and specificity, allowing the reader to understand the context and intention behind the phrase. With the right synonym, any writer or speaker can more accurately describe a character, event, or circumstance.