Timing is everything and in few places does it matter as much as in cooking.
Underdone, overdone, or perfectly done is all a result of timing. It's a basic that often gets overlooked in the process of chopping, marinating, basting, and otherwise agonizing over a meal. Freshness of ingredients also matters. Timing in cooking and food preparation to me is analogous to a teenager driving a car alone for the first time. You know where the mall is, you've been there a million times, but you have no idea on how you actually get there when driving yourself.