Yogi Bhajan on sadhana. Lots of great quotes on sadhana: "The greatest reward of doing sadhana is that the person becomes incapable of being defeated. Sadhana is a self-victory, and it is a victory over time and space. Getting up is a victory over time, and doing it is a victory over space. That is what sadhana is. And when you do a sadhana in the sangat, you enrich yourself in multiple ways."