Motivation.
Unfortunately, you can’t rely on just feeling motivated to do well in an extra subject. By the time the Christmas and Easter tests come around, you’ll be so caught up with all your other subjects that you might start to neglect your extra classes. Hence, you need to have a solid reason why you want to do an extra subject, beyond just ‘feeling like it’ in September.
Here are some good reasons why you’d want to do an extra subject: