No single theory of motivation that psychologists have come up with can singularly explain what motivates humans to take action. Here are a few examples of different theories of motivation at work.
According this theory of motivation, people are motivated to behave a certain way simply because they are biologically programmed to do so.
This theory proposes that people are motivated by cognitive forces, such as have been condense in the famous Maslow's Hierarchy of Needs. In this hierarchy, needs are ranked from physiological, safety, social, and esteem needs, which all leads the ultimate need of self-actualization being fulfilled. Why do I think of P.K. Subban when I think of self-actualization?
This theory states that we establishes desirable outcomes that we are motivated to achieve based on our expectations of the future, and judgment of our own instrumentality of achieving that goal.
Thanks for reading! I will probably re-visit some more theories of motivation in the future, so keep your eyes peeled!