How are 3D animations so detailed?

(Note: I’m NOT an animator lol! Just have a question!)

I was watching TADC the other day and was very impressed with all the tiny facial expressions and detailed movements of the characters. How are 3D animations created with such detail? Is it entirely manual? And how long does it take to make (let’s say a ten second clip of two characters chatting)?

Thanks for helping me understand, it’s very impressive what you guys can do!