The X Factor is a special talent or quality that makes you stand out from the rest. What gives someone the X Factor? No one knows, and that is exactly what the "X" stands for. It's that "thing" that makes you stand apart from your counterparts, what ever that thing may be.
Singing competitions are looking to separate the simply really good singers, from the singers with the X factor. Publishers are looking for that writer with the X Factor as well. It's the thing that will make people want your product. There are millions of great singers and writers, but the X factor determines their success. As a matter of fact, if you look at the very successful, often they aren't the best singers or writers, but the most entertaining because of that X factor.
That's why it's so hard for us, as Christians, to not try to earn God's love. The world says, "You don't have the X factor." You have to be the best. There's only space for #1. Jesus says, "who ever believes in me has eternal life." WHOEVER! You don't need the X factor, you don't need to be the best. You just need to believe in Him. And that's confusing to us who are used to living in a world that only looks out for #1.
I don't have X Factor. But I do have J Factor - Jesus. It's for all the rest of us. I'm not the best, but I believe in the one who is. I'm not perfect, but Jesus thinks I'm to die for. And he feels the same way about you.