Value, value, getting value to users. Work on the most valuable thing, always. You could probably summarize the Agile philosophy as "deliver value to end users faster." What's the next most valuable thing we could work on, get it done, and get it out to production.
With a sprint cadence, we commit to a strategy for two weeks, we work as a team through the items in our sprint backlog, and we retrospect at the end to talk about how we did. There's always the chance that some circumstance around the business could change mid-sprint that may change the team's idea about what is most valuable to work on in the moment. Since sprints balance consistent delivery with optimal value, we keep our heads down and finish the chunk of work we agreed to deliver at the start of the sprint.
This requires leaders and engineers to get used to telling people outside the team, "That's a great idea! We'll put it in the product backlog. We can start working on implementing this idea in less than 2 weeks from today!"
As arbitrary as the sprint cadence can seem, I see the sprint as a delivery protector--a built-in reason to say not right now. The items we're working on today may only be 80% of optimal value, but we're going to finish them dammit. In no more than two weeks we can shift our strategy 180 degrees if necessary, but not today.
