To keep to oneself, to be secretive, to be very cautious in one's dealing with people and giving nothing much or nothing at all away. (As if one were playing cards and not permitting anyone to see any of the cards.)
"He is very cautious. He plays his cards close to his chest."
"You seem to be playing your cards close to your vest."
When you fail at something in life (eg. failing an exam or not getting a job), go home and spend an hour just standing in the shower, propping yourself up against the wall with your eyes on your feet.
Caleb knew the only thing to do after he didnt get prefect was take a failure shower.