I met Bobby Flay at the South Beach Food and Wine Festival and asked him to please clear up this mystery, as I'm starting to hate cooking chicken. He said by far, the most common reason for tough chicken is overcooking and better to leave bone in and skin on. I was lucky enough to eat his fried chicken breast that took him about 10 min to make. Juicy and tender of course! I have also stopped using frozen chicken because that seems to be worse. I also avoid large thick breasts. I pound it so it is more uniform and takes less time to cook. A quick sear on high heat to get some color. Then into a 350 oven for about 10 min. Still, the most tender fall-off-the-bone chicken comes from poaching, like making soup. For this, I put a whole fryer into a pot along with veg, etc., cover with water, bring to a boil, reduce to a very low simmer and cook covered, for 1 hour. Great for making chicken salad too. Good luck!