The path Arjuna is about to walk is not untrodden. Many seekers before him let go of attachment, fear, and anger, absorbed themselves in Krishna, took His refuge, and through the fire of knowledge became purified. They attained Krishna's own nature. Old footprints on a mountain trail tell a climber: others have made it to the top.
Attachment, fear, and anger — these three are the great obstacles. Attachment ties a person to outcomes. Fear paralyzes action. Anger distorts judgment. When all three subside, the mind becomes still enough to receive knowledge. And that knowledge, like a refiner's fire, burns away impurities until what remains is pure.