I describe the agile process as sustainable development. The idea is that development should be able to be continued indefinitely. This is a big change from the usual development approach of big pushes and lulls.
It's a old habit, and old habits die hard. We know we can push harder at times to get over a line. And as individuals, we suffer for doing that. We run the risk of burnout.
We recently jumped deep into a problem that was complex and time sensitive. It required a big effort to get it over the line. At the end of it we made it, but it came at a cost. The following sprint has been deflated, with tired developers, a lack of enthusiasm and focus, and inevitably more mistakes.
The scrum process is set up to avoid this. That we agree to take in what we can handle, and base what we take in future sprints from past performance. We learn what we can achieve from what we have achieved. So those moments we go above and beyond throws that out.
It's an achievement to deliver 4 weeks of work in 2. But if the cost is tired unmotivated developers, there had better have been a very good reason for doing so.