Babies and toddlers are learning though observing adults. They can't observe there own behavior and learn though self-analysis.

I let my 14 months old daughter watch two cartoons today, one was about cat and mice (Russian cartoon "Kot Leopold") and the other one was about a monkey mother and her babies. I can definitely see myself in the character of the monkey mother and my baby in the characters of the baby-monkeys. http://www.youtube.com/watch?v=rd1dQXhgNEk&feature=related
The interesting thing is that my little one was not interested in the second cartoon at all. 

25 months and reasoning

I've noticed that my toddler understands the not to-dos supported by reasoning and changes her behavior. For example, when I just say "don't do this or that", the "no" would mean nothing to her and would not change her behavior. However, if I explain to her why it is bad to do this or that, she stops doing this or that. So, it looks to me like the reasoning helps my toddler to understand why she should not do certain things and change her behavior.