Why are some people able to cut through their own motivations and just try to see the facts as objectively as they can?

The answer is emotional. The soldier mindset is rooted in emotions like defensiveness or tribalism, the scout mindset is, too. It's just rooted in different emotions. For example, scouts are curious. They're more likely to say they feel pleasure when they learn new information. They're more likely to feel intrigued when they encounter something that contradicts their expectations. Scouts have different values. They're more likely to say they think it's virtuous to test your own beliefs, and they're less likely to say that someone who changes his mind seems weak.