How do I animate subtle emotional moments that feel real?

You can bring characters to life, which means you already have the hardest fundamentals. The subtle emotional beats elude you because they are the most demanding thing in the craft. A big action reads easily. A small true feeling in the eyes is the work of a lifetime. Struggling there is not falling short. It is arriving at the deep end. Subtle emotion is hard to fake because it comes from observation, not tricks. The tiny hesitation before someone speaks, the way a real face holds two feelings at once. Animators who nail it are really students of actual human behavior. They notice what most people miss, then put it back frame by frame. Start watching real people and good actors with the sound off, just studying how feeling moves across a face. Take one small moment you observe and try to rebuild it in your work. Then another. That patient study of the real thing is how the subtle moments stop eluding you. You are training your eye, and the hand follows.