Basically, my definition of positive thinking is that whenever you face a difficulty or an obstacle, the first question that comes to your mind would be:
What can I do about it in order to make it work?
And that’s simply a much better investment of energy than the negative questions like “Why am I so unlucky?” or “do I really want to do this?”. Any of those are simply a waste of time and energy.
As with everything, balance is key. Constructive “negative” questions should also be asked once in a while for reflection and a better self-awareness.