Positive thinking widens cognitive array whereas negative thinkins narrows it.

You are on bicycle and you are leaning one way as you cycle along.

Let us think of this 'lean' as your bias toward negative thinking.

Someone informs you that if you just adjust your bias or lean towards negative thinking and straighten up your bike you would accrue great benefits.

Many studies have shown that there are cognitive limitations of negative thinking, ie the high arousal states of anxiety and fear, these place such emotions in the limbic province of the brain and narrows one's cognitive possibilities ie flight/fight.,

Whereas positive thinking widens one's cognitive array.

　

Positive thinking produces a broad flexible cognitive performance to integrate diverse material this is triggered by an increase in the brain dopamine levels partially in the prefrontal cortex and the anterior cingulate which are thought to underlie better cognitive performance (Ashby Isen & Turken 1999)

Whereas negative thinking narrows the scope of attention.positive emotions broaden the scope of attention widening the array of percepts thought and actions