One reaps misery for his senses being not controlled. One acquires happiness on account of his senses being restrained. Therefore, a person should control his mind by self-exertion from objects apprehended by the senses.
प्रसृतैरिन्द्रियैर्दुःखी तैरेव नियतैः सुखी। तस्मादिन्द्रियरूपेभ्यो यच्छेदात्मानमात्मना॥