Welcome to the forums.
First of all, it is very good that you have registered in the forum and asked a question. I can only recommend that you read the Game Tips on the game homepage.
http://www.mmarmy.com/tutorial.phpEDIT:
You can find it also here:
http://www.mmarmy.com/forum/ubbthreads.php?ubb=showflat&Number=476725#Post476725Unfortunately, it is not as simple as you imagine.
Like SbrbnHstlr and Trite already said: there different type hiddens.
Maybe your fighter has very good stats in JJ, but his Sub Offense (Hidden) is just not good enough to beat an opponent with good Sub Defense (Hidden). Therefore, your fighter may lose.
Here is a list of all Hiddens:
http://www.mmarmy.com/forum/ubbthreads.php?ubb=showflat&Number=457100#Post457100Looking at the big picture, this game is about the management and interaction of stat builds, style match ups, and hiddens.
Again, I encourage you to read the tutorial on the main page of the game.