Here is a lecture by the Siri Singh Sahib, Yogi Bhajan at UCLA on March 27, 1972:
This is an excerpt based on this lecture, which was shared in The Aquarian Teacher Level 1 Teacher Training Manual:
Each student of yoga must confront the mental attitude of insecurity and doubt. Actually, there are two mental styles we can use to go through life. In one style, we act as if everybody were saints until proven thieves. In the other style, we act as if everybody were thieves until proven saints. Which style of life your mind uses depends on the strength and balance of your nervous system.
People who live the first style walk through every wave of life with an even attitude. If you ask them, “How are you doing?” they reply, “I am fine.” If there are certain dangers they might encounter they say, “I don’t care. No danger is going to bite me.” People who live by the second style are completely different. If you tell them, “The road is clear. It has been checked. It is beautiful,” they will say, “I don’t believe it. I can’t walk further.
This powerful insecurity can create problems and disrupt happiness. The roots of the insecurity often run deep into the core of the elemental personality of a person’s consciousness. Meditation, Kundalini Yoga, and White Tantric Yoga all work to disentangle the threads of insecurity from the layers of the subconscious. When these are removed you can deal with things as they actually are rather than as your fears portray them.
In every mental state, the subconscious plays a major role which we are not aware of. We say, “I know my past.” Actually, there is no such thing as “my past.” That past is only the experience you have in your subconscious mind. You become attached to it, and this prevents you from moving forward in your life. In Kundalini Yoga, we fry this subconscious mind; we make toast out of it and eat it.
We have a technical know-how to approach this subconscious mind. If you do not clean it out, it sits behind your conscious mind and does mischief. It sits in the back and can spoil the image of human life by repeating experiences which are already in the past, but which are recorded in that subconscious mind. The subconscious mind must be taken care of and trained with Kundalini Yoga to be an aid in life.