It can drive the most even-tempered person to a boil. You follow the grilling instructions only to find your ribeye or filet undercooked or overcooked. Maybe you got a phone call, or were caught up watching the big play in the TV room while your steak burned outside. Grill thermometers were built for such occasions. Grill thermometers can tell you what the instructions cannot, namely whether your grill runs hotter than the instructions account for, colder, or just right.