Real obstacles or destoyers of Calm Mind are fear, suspicion, hatred, anger, greed. These emotions are the opposite of a calm mind. Calm mind sees things more clearly, more realisticly and more holistically.
More self confidence means less fear; if we have a more objective mental attitude we feel less greed, we feel more content.
How to develop self-confidence, or inner strength: once we have developed a compassionate or altruistic attitude then there’s no basis for fear.