As for what makes this insincerity grow and arise – this is interlocked with Emaan and the healthiness of the heart. The healthy, Eman-filled heart is conscious of Allah, and fearful of His anger, and aware of His gaze, and afraid of His threat, and vigilant of the nearness of the Last Day – so it’s sincere. The diseased heart sees things blurry, sees the Day of Judgment as far off, forgets how closely Allah watches the eyes and hearts, and prefers the enjoyment of this life (praise of people) over the next.

— Abu Abbaad