There are different causes of job burnout. They include:

Lack of control. Not having a say in how you do your job, such as your schedule, assignments or workload, can lead to job burnout. Not having what you need to do your work also can add to burnout.
Lack of clarity about what's expected of you. If you're not sure what your boss or others want from you, you're not likely to feel like you're doing a good job.
Conflicts with others. Maybe you work with an office bully. Or you feel that co-workers are against you. Or your boss is too involved with your work. These conflicts can add to job stress.
Too much or too little to do. Maybe your job is boring. Or it's so busy you can't keep up with the demands. In these situations, you need a lot of energy to stay focused. This can lead to fatigue and job burnout.
Lack of support. If you feel alone at work and in your personal life, you might feel more stressed.
Problems with work-life balance. Problems with work-life balance. Maybe your work takes up so much of your time and energy that you have nothing left for family and friends. This lack of balance can lead to job burnout.