We get annoyed about having to learn genders of words in other languages. It's just so silly! Then you remember that millions of children pick it up every day.
Nothing in language can actually be hard. It just takes enough practice to start thinking like a native.
But note I said practice, not repetition. You have to want to do it correctly. If you have an ear for correctness you will get there.
Native children spend thousands of hours learning language. Just because a child can do it through some of the greatest effort of their lives at that point doesn't make it easy surely?
I definitely didn't mean to say learning languages as an adult is easy because children do it. I've always thought methods like Rosetta Stone are complete crap because, as you say, we don't have thousands of hours to put into this like children do.
But what we do have is the most powerful tool we know for learning: language! Adults use their already acquired language to make learning a new language easier.
What I really meant, though, is there's nothing fundamentally "hard" about most things in everyday language. Being "hard" is quite hard (heh) to define but some things are intuitively hard, for example, playing Stravinsky's Petrouchka is always going to be considered a remarkable achievement for a piano player. But natural languages aren't like this. They are almost by definition easy because they are natural. If it was hard people would figure out an easier way to talk.
Nothing in language can actually be hard. It just takes enough practice to start thinking like a native.
But note I said practice, not repetition. You have to want to do it correctly. If you have an ear for correctness you will get there.