There's an article by Adam Alter on the New Yorker website that debunks the claim that "positive thinking" is the key to happiness and success in all things. In fact, Alter says, data show that unquestioning expectation that things will go your way may make you less happy and successful. You may work less hard, for example, and also be unprepared when things don't go your way. Relentless optimism may not help you heal from injuries, either.
This doesn't mean there isn't some truth in the benefits of positive thinking. Someone who projects confidence and optimism will likely gather more friends and supporters than someone projecting gloom. And, of course, our thoughts generate karma just as much as our words and actions. Thoughts can be powerful. But that doesn't mean optimism of itself will bring you good luck.
Of course, we could ask "What do you mean by happiness?" and "What do you mean by success?" In Buddhism, happiness is a mental state cultivated by practice that does not depend on an object of happiness. In other words, it doesn't depend on what happens to you, or what you acquire. His Holiness the 14th Dalai Lama said, "Happiness is not something ready made. It comes from your own actions."
And what is success? We've all heard of people who are never satisfied, no matter how much power and money they acquire. They are like asuras, the jealous gods, always driven to get more and more and more. What good is it all if it doesn't satisfy? True success may be doing work you love doing and enjoying what you have, even if it isn't much.
The famous best-selling book The Power of Positive Thinking by Norman Vincent Peale was published in 1952, so it's been around almost as long as I have. That book is said to have touched off the self-help industry, although I suspect there has been a lot of 'self help" in American culture long before that. Still, it seems ever since there has been one book or program after another that promises to unlock the secret to happiness and success, including The Secret. Everyone wants to sell you the secret decoder ring to life.
Of course, as long as it's a trick, just a way of re-arranging your mental furniture, it may give you a temporary lift but in the long run it's not going to work. It's like those link-bait ads that pop up on the Web all the time -- do this one simple trick and ever diet again! If you actually click on the link you are subjected to a sales pitch that never tells you what the one simple trick is, and in fact the program being sold appears to be more complicated than "one simple trick." But it made ya click, huh?
Maybe success and happiness is where you are when you don't feel compelled to click any more.