The Secret is basically a dumbed down summary of how Neuro Linguistic Programming can work
Basically it comes down to 2 things, our belief system and conscious awareness.
If we are restricted to operate within our belief systems (you must work hard to make money) Then you will unconsciously
put yourself into that situation (working hard to make money) The opposite is also true if you believe (money comes effortlessly)
Unfortunately, changing a belief system is not always easy as it needs to be repetitively affirmed before the unconscious accepts it as fact.
When you think about something.. say a blue car... you are telling your unconscious to bring 'blue cars' into your conscious awareness.
The Secret sells itself on the idea if you just think about being rich.. money will get dumped on you from the sky in millions.. In reality, at best
this 'free money' often materializes as 'noticing' discarded coins on the ground etc..
So basically it works but only if your thoughts agree with your core belief system