“You get what you think about, whether you want it or not.”
— Esther and Jerry Hicks, Ask and It Is Given

There is a device at the base of your brain called a reticular activating device whose job it is to filter out information that we have concluded is not important and assists you in noticing the things that you have decided are important. Another way to see it is that it works in conjunction with your belief system.

For example, if you have decided that the world is full of mean people, you will primarily notice all the mean people in the world. If however, you have made it a belief that the world is full of love and miracles, you will notice more love and miracles than someone who believes otherwise.

This is also the Law of Attraction in work. Because you get what you think about, even if it is a negative thought (mean people) you will actually attract (and notice) more mean people in your life.

So do this experiment: Focus only on the things that make you feel good. Take an important relationship in your life that may not be as optimal as you would like it to be and focus only on the positive aspects of that person for one week. You will notice their behavior will actually change positively as well.