From the perspective of these teachings, why might someone fail to realize the Self, and what is the key to success?

According to the wisdom in Chapter 37, one might fail to realize the Self because of the persistence of desires, which act as seeds for rebirth, and a strong attachment to 'body-consciousness'. This is the knot in the heart that binds a person to sorrow. The key to success is twofold. First is the renunciation of desires, which leads to union with the bliss of Brahman. Second, and equally crucial, is the cultivation of "full faith and patience." These qualities are personified as divine grace, without which the Lord dwelling in the heart cannot be seen. Therefore, success hinges on coupling the pursuit of knowledge (Brahma-Jnana) with unwavering faith and perseverance.