The Difficulty of Positive Thinking

It is funny how the hardest things in life are most simple in theory. I had this interesting chat with my brother-in-law who is this positive, uncomplicated guy who told me how being positive is a matter of practice. He said that naturally when you want to do something, it is the habit of your treacherous mind to come up with ten negatives as to why you can't do it, but he told me to try it the next time. He said the next time I wanted to do something, I should try keeping it as pure thought, undiluted by negatives or mental obstacles.
What he was trying to tell me was how great the power of "pure thought" is. When you have a vision and you really believe that it will happen, the elements of the universe come together to make it happen. Say I want to write a book and publish it. I should, according to this theory, just visualise deeply in my mind, a printed book, my printed book. Then without having any thoughts I should go on with my life, autosuggesting to my subconscious, now and then that I will publish a book. And lo and behold, it will happen. It may take 10 years but as long as I am wishing for it to happen, not giving excuses about why it won't happen and thinking "pure thought", it will happen.
And this theory further states one person is no different from another.
"But what about the chemicals in our brain?" I shouted. I probably felt that if I shouted I would convince myself. "Each one of us is made differently. You are not allowing for human frailties".
He grinned and said," See you are already creating an obstacle. The chemicals you have are created by the positive or negative thoughts you have".
All my delusions came crumbling down.
Bah! I had just got comfortable with the idea that my life was difficult.