Karma, in the popular view, is often perceived as the bogey man of Eastern philosophy, as the stick that punishes you for doing the wrong thing. In reality it is much simpler than that, and it carries no judgmental overtone at all.
Karma is simply reflectance. Reflectance is a property of the universe. Therefore, life reflects what you project. This principle of reflectance or karma states that life reflects your beliefs, emotions and actions. The stronger these are, the more apparent it becomes that life is a mirror of whatever you project.
Whenever you change the way you view life, the universe, just like a mirror, reflects your new view of reality. This may not occur instantaneously as, often, circumstances do not allow the new reflection to immediately manifest. In this case, the new reality is held, like a pressure within the aura of your body's subtle magnetic field. You then walk around in life, surrounded by this magnetic potential, your "karmic pattern," as it influences your circumstances to adapt into a form where the new reality will be able to manifest and operate.
Reflectance, sooner or later, produces manifestation. Therefore, if you don't like something in your life, the most powerful way to change it is to discover how you have generated that reflection. Then change your point of view - the beliefs, viewpoints and energies that you put into your life - so that the reflection is changed.
It's just like the law in physics: "For every action, there is an opposite and equal reaction." This law goes much deeper than just a law of mechanical motion. It is how the universe is designed at all levels.
Reflectance is entirely automatic. There is no judge. No one looms over you, threatening retribution for imaginary sins. However, because this law of life is automatic, you have to be the one to initiate change. It will not come to you until you take the initiative, until you create the action so that there can be a reaction.
If you seek more happiness from life, the mirror of life will shine more happiness back upon you, just as soon as you decide, within yourself, to become a happier person. Then it will reflect your new reality.
Your power lies in how you respond to the circumstances which have been created in your life. Circumstances, within themselves, are inherently neutral. It is human judgment that assigns positive and negative values to those circumstances. It is a paradox of life that the challenges of difficult times can produce the most happiness in the end.
Remember that if "bad" circumstances are affecting you, it is often not because of some "bad" way that you thought or behaved in the past, but because you planned your life so that it would present certain challenges. How you respond to those challenges is the whole point of the exercise. The strongest steel is that which is quenched from great heat and the most compassionate heart is that which has seen great suffering in the world.
Your viewpoint is your response to the picture that life presents, and it is totally under your control. Your viewpoint determines what energies you will put into life and therefore what the mirror of life will reflect back.