MG, what causes it?

For 12 years I've been asking, what causes MG? How / why did I get it.
Always gotten the same answer, we don't know. It's not viral, and you can live with it, provided I follow my doctor's advice, keep taking my meds, and lead a normal, clean living. But then again, these same parameters apply to everybody else, all I want to know is, why me? Why MG?