A lot of people are afraid their chicken is not going to be cooked thoroughly so many times they end up overcooking it as they are afraid of getting sick. Often times you will see chicken breasts in the oven being cooked at 350 degrees for 45 minutes. That's too much. I go higher on the temp and lower in time. 450 degrees and max 20 minutes in the oven and they come out great. Smash the breast down before cooking to an even thickness all around. Hell, if I'm cooking them on the grill at 400-450, I only leave them on for about 5 or so minutes on each side. Meat thermometer is a must have tool imo