As an individual contributor in software development, the job is sometimes stressful. Bugs can be hard to find and elude you for hours. It's a matter of logic because a computer will only do what you tell it to. With a bug in your code, your assumptions are wrong. You change your premise and then the code to match.
As a manager, the job is sometimes stressful. Leading people is about debugging humans, and people aren't logical. Correct assumptions don't lead to desired outcomes because people don't do what they know is logical. The beliefs and premises are not yours alone, and it's nearly impossible to change the code in someone else's head.