People who wear their heart on their sleeve express their emotions freely and openly, for all to see. They do not hold back their emotions, for good or bad. They let things get to them easily. There is a possibility of not knowing how to let go of negative feelings and unhappiness.
Therefore, once they fall in love there is an opening for ridicule. People tease them. The heart brakes. Difficulty hiding the wounds close to the chest and in privacy. A bit like a card player not wanting to show their hand yet unable too. Therefore, ‘giving up the game’ and exposing his own bluff. In life, there are lessons to learn. One is to “keep your cards close to your chest”, which figuratively means not displaying emotions or what the objectives are.