I've never gotten burned out from working too hard. I get burned out by having no say or control over what we are working on or how it's done, and by getting stuck working on low-value tasks for prolonged periods of time. Those projects are the ones that make me not excited at all to come to work.

It's usually because the client / product owner has no idea what they're doing but still insists on making all of the decisions with no input from users / developers / designers. And it sure sounds ridiculous, but it is the norm. Developers are viewed as people who do not want to participate in meetings or planning, and who exist on streams of work to do. If the developers run out of work, they'll go crazy! As long as we "keep them unblocked" and have tasks ready for them, we're doing our jobs and they'll be happy!