A human being can lift 1,000 kilograms
Scientists have calculated that if all the muscles of a normal person were ALIGNED so they all pulled in the SAME direction, then that person could lift 1,000 kilograms!
Now, the human mind has often been compared to a muscle ("exercise it to make it stronger", etc.).
However, unlike muscles of the body, the mind can be aligned to focus all of a person's mental energy in ONE direction.
This is why goal-setting is so important. It channels all your thoughts and mental energy toward ONE point, thereby multiplying the efficacy of your mental power.
Unfortunately, we live in a society where there are so many distractions (marketing, news, etc.) that our mental power is continually being diluted. Mass messages from the news, magazines, advertising, etc. continually DE-STRATEGIZE people's lives (that is, these mind-numbing marketing messages make people FORGET about their goals, so that they become more easily controlled by advertisers).
Smart and successful people don't fall into that trap. They rarely watch popular TV programs, the news, or other low-value information sources. Instead, they read books to strengthen their minds continually. They know that distraction is destruction. Destruction of a person's mental power.
What does all this have to do with The Secret?
Well, the documentary says that you should visualize your ideal state, your ideal future. This is like goal-setting. If you do the exercise honestly, you will have a single point toward which you can direct all your mental energies, attention, focus, etc. This, by itself, will make you a tremendously effective person. You will naturally focus on the important stuff (which brings you closer to your goal). You will naturally ignore anything or anyone who does NOT help you get closer to your goal.