There's an upside-down U curve relating performance and arousal
When optimizing for focus there is a goldilocks zone for arousal. The “optimum” level of arousal for focusing on a particular task depends on the task. If you’re writing, you would probably want a relatively calm and even-keeled level of arousal. If you are powerlifting, you would want to be considerably more hyped.
Experimental Evidence
An experiment had sleep-deprived people and well-rested people perform a task. The well-rested people did better, which is unsurprising. However, when loud aggressive music was played, the well-rested people started performing worse whereas the sleep deprived group started performing better. The experimenters’ hypothesis was that the well-rested group shifted out of the optimum level of arousal, whereas the sleep-deprived group got closer to it.
