sides for bacteria to harbor, so cooking it rare or medium-rare kills the bacteria on the surface of the steak.
the third "secret" to perfect burgers is how to gauge when they are ready to flip. when you place a burger on the grill or in a skillet, look for blood to come to the surface and then turn them over. blood will come to the surface again and when it does, it's cooked to medium.
the final "secret" to a perfect burger is simply do not press down on the burger when cooking. this literally pushes all of the juice out of the burger and is a huge "no-no." 