Such a needlessly extreme example, sometimes it might mean just working on the backend after doing nothing but frontend for your career, sometimes it might mean

Such a needlessly extreme example, sometimes it might mean just working on the backend after doing nothing but frontend for your career, sometimes it might mean not assigning a feature of a certain complexity to the person you know likely grasps it instantly and assigning it to someone who you're less sure about but wants to do more. It can be just as much about figuring out and cultivating the potential of your workforce and that can create greater efficiency over time. There are certainly opportunities where this can be accomplished, because if everything is mission critical, business itself is doing something wrong. The amount of opportunity and the nature of such will vary across businesses, and perhaps an engineer may need to go elsewhere to search out further challenge. Your statement that "Minimizing one challenge frees mental processing power to worry about bigger issues" presumes a level of uniformity.