sincerity

(n) an earnest and sincere feeling earnestness, seriousness,
(n) the quality of being open and truthful; not deceitful or hypocritical
- his sincerity inspired belief
- they demanded some proof of my sincerity
(n) a quality of naturalness and simplicity
- the simple sincerity of folk songs
unassumingness,
(n) the trait of being serious
- "a lack of solemnity is not necessarily a lack of seriousness"- Robert Rice
serious-mindedness, earnestness, seriousness,

earnestness seriousness unassumingness serious-mindedness

insincerity falseness hollowness frivolity frivolousness