When you are positive, you push away the negativity. And when you are negative, you cut off the positivity. 

In the first case, the mind is clear as water: the ideas are clear, the solutions are ordered and logical. In the second case, is more like petroleum. Black and dense, and the ideas are a condensation of problems without solution.

 One piece of advice, be positive to have clear ideas. Only later, work on those ideas to become the best version of yourself.