Why are writers usually influenced or inspired by pain?

Every story requires pain and suffering. Pain develops character and has a sensuality of it's own. In some ways suffering ceases to be suffering at the moment it finds a meaning, such as the meaning of a sacrifice. Pain and suffering offer a starting point for reflection on human existence.

YES THATS TRUE,,, BECAUSE ALL THE BEST POETRY , NOVELS , OTHER CREATIVE STUFF WAS WRITTEN IN MELACANIC MOOD I.E SAD , PAIN.   YOU KNOW CREATION IS ALWAYS MCOUPLED WITH PAIN,,, JUST THINK OF YOUR BIRTH.

I don't know.

pain and creation are associated with each other,,, creativity demands pain .

If you noticed you will find most of successful writers suffered from pain in their life which made them so sensitive like for example,Oliver Twist ,Shakespeare, Taha Hussain and many other. And I believe that pain and sensitivity are two things that create or make a good writer.

There is a saying in Tibetan, 'Tragedy should be utilized as a source of strength.

It is not the inspiration but in actual they take out the pain stuck in them, it is a way to relieve the pain . People like it because they can relate to it easily. 

Dear Samar it is really good and real point that most of writers 

I think this is because of pain and hard times effect that give each one of us a kind of alarm or chance to spend time with himself. This time mostly leads to brilliant ideas and rich feelings and experiences that we need to share with others 

Firstly, because writing about "pain" or its other synonyms "disappointment" or "anger" is therapeutic. And I'm only stating a fact that is backed-up by science. I truly believe that most (drama) writers sought writing as a way of ventilating their inner feelings at a younger (or later) age for the sake of releasing such thoughts, before they became masters of translating feeling, observation or imagination into words.

Secondly, people are more tempted to write about "pain" than about "joy", seeking solitude & solace at the same time. This could be the case because the latter emotion, joy, is easily shared with people in all extroversion and is more accepted or applauded by most people. (People mostly avoid sad or negative people & like to listen to and see the happy ones).

Lastly, writers learn by experience & by being "book worms" themselves in most cases, that "pain & drama are nice", regardless of how paradoxical this sounds! Drama books are more likely to become best-sellers than others. People like to read through the upheavals that drama carries, either identifying themselves with it or just enjoying the entanglement in dramatic stories in search for an expected climax, that gets them gasp in unexpectedness, amazement or blissful happiness!

Its because writers are mainly cold blooded, And they have been many bad things in life which they cannot change ...hence they come to a conclusion to share there hardships through there writings.....because a pen can do that which even a sword wont....!

cause people when theya re happy they don't usually write about it :)