Random thoughts, thoughts that enter your mind through no deliberate effort of your own, are predefined, because these thoughts are generated by the feelings you feel and the experiences you interact with. In other words, once the vibrational frequency of your feelings and the vibrational frequency of your experiences has been established, they then generate partially randomized thoughts of an associated nature.
Thus, through the use of deliberate thought, thoughts created through deliberate effort, you can decisively alter the direction in which these randomized thoughts take you. As you purposely direct your attention towards your desires and align with them, random thoughts entering your mind will also become aligned with your desires as well.
This process occurs, because as you give your attention to your desires, you begin to vibrate in harmony with them and your thoughts and experiences then begin to match your desires since your thoughts and experiences always match the vibrational frequency you are offering, the way you feel. As you interact with various experiences throughout each day, thoughts will be generated based on the vibrational frequency of these experiences, and the way you feel, and any randomly generated thoughts will be a better match to your desires due to the deliberate direction of your thought.