Simply put, animation is the creation of life. It seems to me this definition is somewhat overly simplified. At least, as it pertains to doing it professionally. If we dig a little a deeper than the simple, textbook definition of the word, we find ourselves asking "How the hell do I do that?" The trick is to find
something, whether it be a gesture, a facial pose, a flourishy head tilt, or even a simple, well-timed eye dart. Find something that speaks to who your character is. Show this to the audience. If you get it right, you get the audience to invest in them emotionally, "...believe unbelievable things..." as Brad Bird puts it. What is it about the acting choice that you've made that speaks to who that character is and where they've come from in the context of the film? This is true of great acting, not only in animated film, but live action as well. It's also true in life. How does your girlfriend/boyfriend act when they get angry? How does that differ from how your brother/sister act when they get angry? For me, animation has been the search for life, and not the creation of it. Seek out the things that make people who they are. Put that into your work. It's the discovery of these things that is the most difficult, and the most satisfying when done right. Maybe this is all because I am still learning. But, then again I don't think you ever
stop learning. Look for inspiration any and everywhere.