An important part of leading a development team is detecting and preventing burnout before it sets in. Software development is this strange mix of creating art and worshipping logic. Programming requires you to creatively solve problems yet in the most rational way possible.
After working through a rough project, demanding managers, working a ton of hours, or due to some personal issue developers are very susceptible to burn out. Burn out is usually where your brain pretty much turns off the ability to solve problems creatively. You might be able to churn out HTML all day but good luck architecting a new API or solving a difficult bug. Marissa Mayer also has the unique and valid perspective that burnout is caused by resentment.
The best way I've found to prevent burn out is to create a fun environment with as little stress as possible, give the developer more personal time, and if burnout starts to set in give them an easy project where they see progress often. Another thing to always guard against is creating resentment, so make sure that you aren't demanding too much and be as flexible as possible. It's amazing what a three day weekend can do to someone's outlook. It's also extremely refreshing for someone to create something and solve a problem without adding to their mental stress.