Let's face it. Characters without some sort of tragedy in their pasts are boring. Too often, they're Mary Sues or have a boring personality.

However, characters that are purely made of tragedy are even worse. I find that, more often than not, if a character doesn't have a nice balance of tragedy and joy in their lives, they - to put it simple - suck.

These characters are often too moody, too annoying and too easy to upset.

Finding Balance

When looking to make your character's past nice and balanced out, start with the basics. That is, the family and friend relationships. If they had a bad home life, give them a close friend or a distant relative they adore. On the other side, if they have no friends, they should have good family relations. If a parent is bad or abusive, have the other one be good.

Next, we look at events. Don't stack tragedy after tragedy on your character. Interspace happy events - meeting friends, getting a girlfriend/boyfriend, etc - throughout their lives as well. This makes the character a lot more realistic and enjoyable, especially when it gives the character reason to not be an obnoxious prick all the time.

Lastly, I suggest structuring the character's priorities properly with their past. If someone values family over all, don't give them a crappy home life. The same can be said for characters who value love, friendship, etc. It leads to an unbalanced character.