Your samkalpa is affected by the subtle impressions of the past and by thought, speech, and actions that you have stored in the chitta, the mind field. Because you have forgotten the subtle impressions of the past, as well as the place where you stored them, they become unconscious; thus, the storehouse is called the unconscious mind.
The material in the unconscious mind affects your samkalpa outside of your conscious awareness. In turn, your samkalpa loses control over the conscious part of the mind.
For example, sometimes you think thoughts you don't want to think, speak words you don't wish to speak, and perform actions that you do not want to perform. Or you postpone certain thoughts or actions. All this is due to the unconscious.
Source: The Tradition of the Himalayan Masters by Pandit Rajmani, Ph.D. Tigunait