okay just
Think about how those normally steady hands must shake when he’s holding a weapon.

I had a friend write a huge analysis on this, I’ll see if I can find it, but you guys also love throwing out headcanons that make me weep how accurate they are, so have at it if you want

He has the steadiest hands in the Fleet. Legendary even. But right now they are shaking violently. Blood thumping in his ears. His knees give out, and he collapsed. He took a life. He had just taken another beings life. 

He had a death grip on the phaser. Tears just brimming, in dead eyes looking straight ahead. He felt a presence behind him, a coat on his shoulders. “Bones” Jim spoke softly, prying the phaser out of his grip. “I’m sorry.” Bones sighed, as he looked down at his hands. Kirk sat next to him, arm around his shoulders, just letting him think. There was nothing he could say. When Bones finally started speaking he looked over at his best friend.

“First, do no harm,” Leonard started in a low, shaking voice. Jim sat in silence as Leonard started reciting the Hippocratic Oath. 

^^^^^^^^^^^^^^