It is easy to constantly be burnt out while also accomplishing very little.
It takes years of practice. You have to build up habits where the line between work and time-wasting is practically blurred. You have to lack self-awareness and refrain from reflecting on your own shortcomings.
Multitasking is a proven method for getting little done. It wastes time by slowing your progress down on every individual task.
Focusing on one task may make you actually complete it. It might give you the momentum to accomplishing another task. This can be avoided by multitasking.
A direct way to exhaust yourself:
To help you get nothing done while feeling exhausted, don't take breaks during unplanned work. Keep struggling.
Do tasks that don't directly accomplish anything. Email and Slack are great for this because neither are directly productive or relaxing. Check Twitter or read the news to get a general sense of anger or anxiety.
One study suggests that working out improves both productivity and satisfaction.
Staying in your chair and moving as little as possible is a sure way to feel exhausted at the end of the day.