When you contain the source of a thought, that thought can change along with you as you acquire new knowledge and new skills.  When you contain the source of a thought, it becomes truly a part of you and grows along with you. Strive to make yourself the source of every thought worth thinking.  If the thought originally came from outside, make sure it comes from inside as well.  Continually ask yourself:  "How would I regenerate the thought if it were deleted?"