I just got into a stupid argument because I said that learning how to play an instrument decently is easy, tedious but easy. All you need to do is practice, but if you have the will, it's just a straight line. On the other hand, I think that writing good songs is not so easy, as it's not a mechanical process or as mechanical. You can certainly become better with "practice", but there's no real defined path to follow.
The person who got irritated by my comment is a neuroscientist... but does she know how to rock n' roll? Doubtful.