It has been scientifically proven that there is a mathematical formula.. Age x last time you had sex = grumpy factor.
Nahhhh...that's not it, trust me
"There is no royal road to this heavy surf-fishing. With all the appliances for comfort experience can suggest, there is a certain amount of hard work to be done and exposure to be bourne as a part of the price of success." From "Striped Bass," Scribner's Magazine, 1881.