Motivation Theory

The individual described in the question is driven by achievement and complexity. This is best explained by McClelland's Achievement Motivation Theory. This theory suggests that individuals are driven by a need for achievement and seek to excel. In terms of other answers, Maslow's Hierarchy of Needs is a theory that identifies basic human requirements and their hierarchical nature, which doesn't speak to motivation by achievement and complexity specifically. Herzberg's Two Factor Theory divides motivation into hygiene factors and motivators; however, it doesn't specifically address the love for challenges and complex tasks. McGregor's Theory X and Y is more about management style and the assumption by management about employees' work attitude, which doesn't match the given situation.

According to Herzberg’s Two-Factor theory, an employee’s motivation and job satisfaction are determined by two sets of factors: hygiene factors and motivating factors. Hygiene factors include elements like working conditions, salary, and job security. Addressing these elements can help prevent dissatisfaction. Motivating factors include elements like challenging work, recognition, and responsibility. When these elements are present, they can actually create satisfaction and intrinsic motivation. The best answer here is thus to first address hygiene factors by improving the working conditions and salary, then enrich the job through challenging tasks. The other answer options either mentioned only addressing one aspect of the theory or not using the theory at all. For example, 'Introduce harder targets...' and 'Make him work on multiple projects...' only take into account the motivating factor, disregarding hygiene factors. 'Reduce workload...' goes against the notion of enriching the job with challenges and so would not likely have a positive impact on motivation according to Herzberg's theory.

Expectancy Theory is the correct answer to this question. This theory, developed by Victor Vroom, suggests that individuals are motivated by the belief that their efforts will lead to desired outcomes.

Key components of Expectancy Theory:
1. Expectancy: The belief that one's effort will result in the desired performance.
2. Instrumentality: The belief that if one performs well, a valued outcome will be received.
3. Valence: The importance that an individual places on the expected outcome.

This theory directly addresses the question by explaining how people are motivated by their expectations of outcomes.

Goal-Setting Theory focuses on how specific, challenging goals can motivate individuals, but it doesn't explicitly address the belief in effort leading to outcomes.

Equity Theory is concerned with fairness and balance in workplace relationships, comparing one's inputs and outcomes to those of others. It doesn't directly relate to the belief in effort leading to desired outcomes.

Reinforcement Theory emphasizes the use of consequences to modify behavior, focusing on external factors rather than internal beliefs about effort and outcomes.

Expectancy Theory provides the most comprehensive explanation for the motivation described in the question, making it the best answer.