In World of Warcraft you have these mysterious things called RP servers. I've ran into more than a few people who have rolled a character on them without knowing what that means, or the special rules that Blizzard has for them.
I try to give them a hand at getting their feet under them and setting themselves up for success in the Role Playing (RP) arena but one subject seems to always cause some pain - character history. Your character history is the story of your character before the game started for them. Since you start as an adult there is all kinds of time to fill in.
But what I want to focus on is why some characters people just accept and others..well...
In large part it boils down to probable vs possible. The first people will generally nod and accept the second at best they cringe and try to RP around you or at worst start complaining how horrible you are for doing it.
Here's an example; I decide I want to play a Half-Elven character.
I decide I'm really the secret child of Syvanis Windrunner and Arthas, an illicit child born out of wedlock and so hidden away.
Anyone who knows much about the game would cringe at that since the odds of it happening are smaller than winning the lottery. The fact the story includes major lore characters makes it even worse.
I decide I'm the child of a human and high elf who met during the wars and fell in love, forbidden by the elven family I was hidden away.
This sets up a nice idea that creates a story within the fabric of the Warcraft story without trying to rip out and retell parts of it.
If there could only ever be one of your character then your character story isn't a good one. Half dragon-half jedi-half orc-monks just aren't something you should try to play. Figure out what you really want from the concept and tone down the weirdness till its something that could walk into the pages of a Warcraft novel without needing to be a Knaak 'special snowflake' character.
Characters have a habit of getting more improbable as time goes on, so its always good to look their story over and edit as best you can to make it less 'WTF' and more 'cool'.