Nice little article that shines light on the psychology of the 2 year old.
"Part of that developmental burst leads to the “no” phase. Our children are becoming their own little people—with their own thoughts and opinions. They are just figuring out that they’re not literal extensions of us, and that separation is essential for them to become functional individuals. That’s why Smerling thinks of this stage the Tremendous Twos instead of the Terrible Twos."