keep one's cards close to one's chest

Because playing cards kept close to one's chest are difficult to see for an opposing player.

keep one's cards close to one's chest

1. (idiomatic) To avoid revealing one's thoughts, circumstances, or plans.
   • 1997, Sabine Rewald, "Balthus's Magic Mountain," The Burlington Magazine, vol. 139, no. 1134, p. 626:

     Balthus has always kept his cards close to his chest. When I asked him if Summertime was a transcription of Poussin's Echo and Narcissus—a variant of his lost copy—he did not reply.

   • 2002, Anil Netto, "Malaysia: Year of surprises and hardships," Asia Times, 25 Dec. (retrieved 25 Oct. 2008):

     Abdullah has not yet revealed his choice for the No 2 post when he takes over as prime minister, preferring to keep his cards close to his chest.