In a musical sense, confidence can translate into a stronger tone, more self-assured entrances, and a better stage presence.
A nervous, anxious player or singer, on the other hand, is likely to have a wavering tone, uncertain intonation, and hesitant entrances.
Since confidence often develops as a person matures and gains life experience, some people may notice an improvement in playing a former childhood instrument that they take up again as an adult.
Again, although such a person may attribute their stronger tone and playing style to "phantom practicing", other factors such as increased confidence may have caused the improvements.
For example, a drummer who abandons music in their teens, and then studies dancing in their 30s may find, if they return to drumming in their 40s, that their sense of rhythm has improved.