Most of the time the things we enjoy doing are based on positive experience that we have had in the past.
If we enjoy a certain subject (for example Maths) it is usually because it is something that we are good at, feel confident with and have been successful at in the past. For a subject that we do not like, (for example English) we may have found this difficult in the past and do not like the thought of having to do that lesson again.
What can sometimes happen is that we only want to feel the positive side of things so we no longer do any of the things that we find hard which makes them all the more difficult when we try!
By understanding what positive emotions feel like, we can use these to try and improve.