It's possible to learn from someone else acting and observing the results only if you understand what the observed person is doing and could map it to yourself. Which babies for example cannot do. They like you making crazy faces but when very young they don't learn how to do the same thing from that. I think for two reasons, first they don't know what you did to make that face (which in the "experimenting yourself" case they would have known even if it was a random action) and second they can't map what they see to actions with their own body. Both need to be learned first before you can learn from observation. While learning from your own (random) interactions with the world is possible from day 1.