When you already have "invested" so much there is no point even thinking about a "fold". You keep playing, till you can, either "raising" if you feel the ball can be hit or "checking" if you are not aware of what is happening. And when things are all done, you wait for the "showdown". You wait till you see cards of all players, and hope that the universe is conspiring for you.
And while doing all this, you bear it all without a smirk, without a frown, hence the term "Poker face". All in.