Thoughts can develop desires and excite the passions. Opposite thoughts of those desires and passions will counteract the idea of satisfying those desires. So, when a person understands this, they will create an opposite thought to help destroy desires and passions.
Think of a person as a good friend of yours and that thought will create itself as a reality. Think of that person as your foe, then also the mind perfects that thought into an actuality.
Neutralize the hostile forces or antagonistic currents with positive thought.
A person who knows the workings of the mind, and controls it by practice, is happy.