When meat is heated, the cells "constrict" forcing moisture out. When you let a steak or roast "rest" after cooking, the cells relax and reabsorb that moisture making the cut nice and juicy. Of course as long as you didn't burn the dang thing. That was one of the VERY few things my mom couldn't cook worth diddly. Chicken was about the only meat that woman made that was edible (was actually fantastic). All others was like cutting up me dang boots and chewing them. And all you old timers out there knows just how tough Dingo boots were!