Breaks (index) are a great way to maintain performance in the long term. The positive effects of a break are overlooked and under-appreciated.
There's a standard break, in which you stop focusing on the task and hand and take a respite to recharge your batteries (ultimately accomplishing more than if you'd just worked continually).
Then there's the Vigilance Break, in which you force yourself to stop and refer to a Standard Operating Procedure or checklist on a frequent and regular basis. These types of breaks are especially important in situations where the stakes are high for failure.