Most people stay closed off to such things by feeling constant anger, pain, stress, or by constantly complaining. Feeling is the key. If you constantly feel anger, you are closed off to feeling pleasure. Your feelings, your emotions expand and create more of that reality for you.
There are many books on the subject. Some of these books were written by doctors, while others came from the minds of researchers. I would encourage you to look at points of view from both of these camps.