What you think, you become. What feel, you attract. What you imagine, you create.
We are a product of our thoughts. It is the nature of the mind to create negative thoughts that have tremendous power. Thoughts of fear and doubts are pathways to failure. Only when you conquer the negative thoughts of fear and doubt will you conquer failure. Unfortunately, thoughts crystallise into habit and habit solidifies into real-time circumstances.
What we forget is, due to our thoughts we are in our current situation. The greatest of the people had only positive thoughts and saw potential in even the most discouraging circumstances. When we have good thoughts, this universe will also reciprocate in the same manner.
Similarly, if you are angry, feeling bitter and thinking how bad is your life or thoughts about ill-feeling towards others, the same things is what you are going to experience around you.
I have always experienced this, during one of my morning walks I saw a cow and an intense love oozed within me. I smilingly called out to the cow. Very sweetly it walked to me and started nuzzling. I caressed its forehead, and it was the most beautiful feeling ever.
The Greatest Battle You will ever fight is that of Yourself.