Dopamine levels are a primary determinant of motivation, excitement, outward orientation, and the willingness to pursue goals.

“So if I were to just put a really simple message around dopamine it would be, there's a molecule in your brain and body that when released tends to make you look outside yourself, pursue things outside yourself, and to crave things outside yourself. [...] But if ever you felt lethargic and like just lazy and you had no motivation or drive, that's a low dopamine state. If ever you felt really excited, motivated, even if you're a little scared to do something. Maybe you did your first skydive, or you're about to do your first skydive, or you're about to do some public speaking and you really don't want to screw it up, you are in a high dopamine state.”