An Intent - A Personification

I am always hidden
yet highly sought after?
I beget every action
but then I cease to matter.
Unless things go wrong!
And then I'm hunted!
They want me, one and all
if only to defend or take offense.
Yet mostly I am a 'pretend'
one that you can't contend,
so well hidden am I.
My covertness on guile depends;
tact with respectable demeanor
which to some the body lends.
Sadly, on my own I cannot fend,
but usually on language depend.
Who I am, and what I become
wish I could control that one.
More oft than not...
a disarming smile,
and I'm undone.
Yet it's me by which people abide;
whether it's life or death, I decide.
Covertly I'm all important,
an overt me, nobody would care.
Sadly, I matter most
when I am not
or don't appear to be.