There is no definitive answer to this unseen power but the law of attraction has been attributed to many thoughts such as an ancient philosophy, karma, or more specifically, an omnipotent universal force. Some sources liken it to gravity or lets just say it simply exists. The law of attraction responds to what you focus on, feel strongly and think about, which ultimately manifests itself into your reality. The upside is a very positive thing yet negative thoughts can result in quite the opposite.
Those who subscribe to the law of attraction claim that it is an inevitable law, like gravity. While, even those who don't acknowledge the law of attraction are participating in it, nonetheless. Before the popularity of the best selling book and DVD, "The Secret", this phenomenon was probably better known as 'cause and effect' but it wasn't as mysterious or interesting as it is now.
A belief behind the law of attraction is the idea that the whole universe gives off certain vibrations. As a part of the universe, you, too, give off vibrations. This is sort of like your personal broadcast, in much the same way a radio transmits sound waves, the law of attraction responds to the vibrations given out by individuals.
If you give off positive vibrations, then the law states you will receive positive things in response. To generate these vibrations, sources say you should visualize reaching your goals and dreams. Every day, you think specifically about those things you want to achieve. Between the times that you are thinking so specifically, you need to cultivate an overall positive attitude so that your vibration will always be positive.
In other words, you can't make up for 23 hours of negative thinking with one hour of positive visualization. Whilst we all have negative thoughts and not a lot we can do about that, we can enhance the process by creating such things as vision boards, reading inspiring novels or just surrounding ourselves with uplifting and positive people.
Like Attracts Like
The law of attraction is based on the principle that "like attracts like." This is why a positive outlook is said to affect you positively, while a negative one does quite the reverse. Are you a radiator or a drain? One who exudes warmth or one who drags you down! Probably not the greatest of examples, but I think you get my point.
An interesting theory within the law of attraction suggesting the brain cannot distinguish properly between observing an event in real life and one within your own mind. To the brain, so the theory goes, an event is an event. It is perceived as being real, even though it is only a thought process. How powerful is that? This is why the law of attraction can turn your thoughts into reality, good or bad - it taps into the very core of your subconscious.
As opportunities begin to come your way, the need to act on them must be your goal. After all, it was your thoughts that manifested themselves. You should be able to distinguish these opportunities from any other ordinary event, especially if they are part of any goal that you have set yourself. People who study the law of attraction follow up on any and all opportunities that have anything to do with their goals, and on those that just intuitively "feel right." After all, sometimes you can't tell how relevant something is to your goals until you act upon it.