Murray

6s are never sure of themselves in the most fundamental of ways; they do not trust their own judgement, and being in positions of authority puts them at risk of scrutiny, which they fear more than any other enneatype (though 5s similarly share this fear, it's just they go about it differently than 6s would & tend to have an unshakeable certainty if they feel competent in their knowledge of something). It's not just the general discomfort of conflict a lot of people have. It's more like a visceral "cowardice" they possess. It causes the 6 to second-guess itself over and over again, even when it's already thought everything through; and it will seek some level of certainty or complete understanding of whatever situation it's in so that it will not be caught off-guard by the unexpected.

6s are well known in their ability to oscillate between a "phobic" and a "counterphobic" state. The phobic 6 is more paralyzed by fear, which is the state Grace is often in when presented with a room full of the greatest minds in the scientific world; he is notably very modest about his achievements, and he doesn't seem to be comfortable sharing his thoughts on a field he objectively has a lot of expertise in. He would rather hide behind an authority figure of some kind - which 6s will do pretty often. They're extremely aware of the social hierarchies around them, and they do their best to conform; they might say what they think others want to hear, or they might try to follow the belief systems others say are the most true. Whatever makes them feel safe.

Counterphobic 6s on the other hand, go against their cowardice. People often confuse this with enneagram 8, but they two types could not be more different.

Anyways, a counterphobic 6 can appear "aggressive" and say or do controversial things to get a reaction, because it's a form of gathering the information needed to come to a fuller understanding of what they're dealing with. A 6 can also move against fear as a means of eliminating any and all possible threats; it's like a preemptive action taken "just in case". For example, a soldier does a patrol at night and hears something rustling in the bushes, and instead of walking away, they might scan for a threat and maybe even shoot the vegetation despite the fact no threat has been found. This is what comes to mind when I think of a more aggressive 6.

I do see some of that in Grace as well; he did make interesting claims in one of his academic papers regarding the necessity of water for other lifeforms to exit, and then insulted another scientist. When faced with the possibility of being wrong, he shuts down. 6s are known to fight fiercely for the things they believe in, which Grace does sometimes, and then not. That oscillation is what makes me more sure in this typing than any other point on the enneagram.