There are many synonyms that can be used for the phrase "lack of success". Some of them include failure, defeat, disappointment, frustration, setback, and unfulfilled expectations. These phrases can accurately describe situations where desired outcomes are not achieved, whether it be in personal or professional areas. Another synonym could be underachievement, which implies falling short of one's potential. It is important to keep in mind that failure and setbacks are a normal part of life, and it is how we handle these situations that determines our future success. Embracing failure as a learning opportunity can lead to greater achievements in the future.