No I'm talking about small mistakes that over time compound the amount of time your team is taking to work around a problem or clean up after it. In order to help your team spend more time working on features and less time working on cleaning up after mistakes you should be doing two things.
I've written before on Sprint Retrospectives before but it's worth mentioning them again as they are the easiest source of improving the efficiency of your team. Sprint retrospectives are a good way to understand what's randomizing your team. They're also a good way to find out why your teams estimates were off (i.e. what wasn't accounted for or what was over accounted for).
The key to the sprint retrospective not to just talk about the problems, but to create action items that will resolve the problems moving forward. After each sprint retrospective you should have an action item list. Each item in the list should have an owner and a due date. This will help ensure that nothing falls through the cracks.
Postmortems help your team identify and correct problems with your process or places where there is no process where there should be. I wrote a good deep dive into postmortems a while ago, but the key to a postmortem is that you use the facts about an incident to see where your process breaks down and identify clear actionable steps to prevent the breakdown in the future.
Postmortems don't have to be used when something catastrophic happens. You can use them to help identify simple things that prevent your team from being more efficient. For example; you can do a postmortem on your sprint planning if your team wasn't able to accomplish all the work they scoped for the sprint. You can do a postmortem on why a feature wasn't built as expected or why a build broke. You can do a postmortem if your team misses a date. There are many reasons you can do a postmortem that don't have to do with a catastrophic event.
The goal is not to do a postmortem for the sake of doing one. But instead to add value where possible by identifying areas of inefficiency and digging in to find out where the problems are and creating actions to remedy them.