Well, in defese of those who dont know how to say it. We may not be lacking reasons, but we have truly known for so long that we dont really think of them often anymore. Like the 70 year old christian who has been going to chuch for decades. You ask his why we thinks christianity is the right religion and not judism or something he probably couldn't really say. Its not to say he didnt have alot of reasons (albiet screwy ones) back when he began chuch, but now its a part of him and he doesnt justify it anymore.
Of course, the dude/chick above has a question make after premed soooo...
Im guessing he/she aint the type.