Imaginative Writing: How Far is too Far?

PTSD victim. Vietnam vet. School teacher.

What is the connection between these words?

They are all labels that describe a character in my latest short story. 

Now, I have written characters that are different than me before, but this is a stretch. Sure, I briefly studied PTSD in an abnormal psych class, read some articles, and attended a reading by Jen Percy for her novel, Demon Camp. (Which I can't wait to read.) But I do not have PTSD, and I am not close to anybody struggling with the mental illness. I am not a war veteran. I have a grandfather who served in Vietnam, but he lives far away, and I have never gotten the chance to hear his stories. I am also not a school teacher. Although I have spent many years in school, I have been a student, and therefore can only guess at what the teaching experience is really like.

This is a problem that all writers have to deal with. We have to write characters that are different from us. If we didn't, our stories would be dull and flat. How can we write a story when all the characters have the same opinions, situations, and experiences? We have to stretch ourselves, be imaginative, and put ourselves in other people’s shoes. But how far is too far? Is there a limit? 

"Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand."

-Albert Einstein 

Should writers heed Einstein's words? Can imagination (with a good dose of research) really substitute for knowledge and experience?

I think the only answer is to start writing and find out.