my mouth shut....am i a loser?

my mouth still shut even i practice......
even though i know how to answer but it seems hard to me to express what i feel...
i still can't speak well, i mean when i debate with someone....
and that made me felt upset....i hate it...
i know what to say,but my mouth shut,the words can't get out of my mouth..
i can do well when it's time for public speaking...i guess..
but to fight with someone?how can i handle this?
maybe i am not brave enough,maybe it's me,myself,
so how can i stand my own choice?
i don't want anybody to change the decision i've made....
when i lose to some one,i can't think about other,
all i know is how to calm my mind....war is in there...
just waiting for the bomb to explode..
maybe i over thinking bout it...
but that is what i felt....
loser!
maybe someday i'll get the answer,from someone who understand me..... :)