I read this quote and it really got me thinking:
"Its unfortunate and I really wish I wouldn't have to say this, but I
really like human beings who have suffered. They're kinder." ~ Emma
I've done my fair share of emotional suffering in my brief 30 years on this planet. I also work every day with clients who have suffered more than any one person ever should. And I realize that I have a sort of... well contempt, though it's a strong word... for people who have never suffered. I think they don't really get it. They don't understand life and as a result can be pretty petty, uncaring, or ignorant. When you're going through something rough, you really don't want Mr. Happy-go-lucky-sunshine in your face. Trust me on this.
But on the flip side of that coin, I see that people who have suffered are almost completely unable to tolerate the suffering of others. Because we've been there. We know.
Buddhist beliefs say that we are all born into suffering and pain, and that we are constantly seeking to be free of suffering, and that we have that power within us- in our minds. Yes. You have the power (I'm now going off on a fantasy book idea tangent.....)
How does this apply to writing? One of the bits of advice that is bandied about is that you need to make your main character struggle and fail. Make bad things happen to them just when they think they've won. Make them fall and get back up and eventually rise above it. Because your readers will connect with and sympathize for a character that has it tough. But its more than that. It's not just sympathy, its the recognition of a fellow sufferer. Someone who hasn't always had it easy, and the realization that if this person turned out better for their pain, then maybe we can too.
Some of the most influential people have pages of suffering and struggle in their backgrounds. Its that struggle that made them who they are. That made them able to see the world through a different pair of glasses than the others around them. Your main character should have that ability. Otherwise their successes in your story will feel shallow and undeserved.