Page 92 - Barbecue Chicken Made Easy

To hit the target temperature you have to remove the bird from the heat when it is 5 to 10°F below target because cooking can continue for 20 minutes or so after you remove the bird from the heat. This “carryover” cooking can take a perfectly juicy chicken breast and turn it to cardboard.
Here's how carryover works: Hot air (convection) cooks the outside of the food. Then the outside of the food cooks the inside of the food by conduction. When we remove the meat from the heat, it continues to cook because some of the heat built up in the outer layers of the meat continues to be passed towards the center while some of it bleeds off into the atmosphere.