When Ivan Pavlov and his dogs led to the discovery of learned behaviour through repeated exposure, and Edward Thorndike discovered the Law of Effect that stated that rewarded behaviours tended to increase, many psychologists were impelled to separate psychology from armchair introspection and formulated their theories as mathematical formulas.
The Drive x Habit Theory. Clark Hull's formula was sEr = D x sHr, which states that excitatory tendency (E) is the result of the drive (D) combined with the habit (H). The drive is nonspecific, such as hunger or thirst. The habit, however, depends on the stimulus (s) and response (r). But the theory turned out to be wrong and even opposite in many cases.
Expectation x Value Theory. Drawing on ideas in economics and game theory, Edward Tolman and Kurt Lewis formulated an alternative account by evaluating motivation based on expectations. Tolman expressed the ideas as the mathematical formula: Subjective Expected Utility = Probability1 * Utility1 + P2U2 + P3U3 + … where subjective expected utility of an action equalled the motivation to act. But, if you expect a reward, why act and not simply passively wait for the expected reward?
Donald Hebb realised that existing theories were too focused on reacting to the immediate environment. Thoughts, ideas and goals could be just as strong for triggering action as sights and sounds.
Together with John Atkinson, they noted that the study of motivation had undergone a "paradigm shift", where motivation couldn't be seen as how actions get started, but how the organism decides to change its behaviour from one thing to another.
Recently, I wrote a piece asking why taking action is hard. Why do we so often struggle to take our ideas and actually do something about them? It's tempting to just say people are lazy or unmotivated, but I think the question is a lot more complex and interesting than it first appears.
Classic goal-setting theory says that you first set a goal, then you make a plan to achieve it and finally you start taking action. Recently, I've begun to question the wisdom of this approach. Now, I'm inclined to believe that, for certain types of efforts, you're better of setting goals in the middle.
Uncertain goals should be set in the middle. This will enable you to set the correct challenge level to maximize effort.
Some research shows that for very complex tasks, goal-setting can hinder effectiveness. This is because complex tasks are cognitively demanding in the beginning and can be frustrating because you can't perform adequately. To add on more tasks can impair your performance.