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.
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.