There are many articles on burnouts, so will link them later on, but a few things to think about.
Typically there are a few reason that triggers burnout in people. Burnout is a chronic state of stress that accumulated over time. Allostatic load is a useful concept to better understand what's going underneath the surface from psychological perspective.
In the context specific to startups, here are a few perspectives on identifying the cause and problem solving them:
When people is running low in a few dimensions of the [[Intrinsic Motivation]], people will get burnt out. Especially, if people feels high-sense of responsibility and does not withdraw/give up on the situtation, it could get worse. Many people will simply quit their jobs, but it's not that easy for [[Co-Founders]] to do so.
For example, if someone feels like they lost autonomy and stays that way for sometime, they will get burntout. This happens frequently when company is scaling fast, and many of their roles and responsibilities become narrower/specialized. What people used to own end-to-end, now needs to be accomplished through influence, delegation, collaboration, and process, it will create the sense that people lost autonomy of that function. The transition can be quite brutal for many, causing chronic stress and burnouts, and people may even go into depression.
Losing hope that things will get better
This happens both in stagnant companie as well as fast growing companies. In the case of the stagnant companies, if whatever they do have little to no impact on the business outcomes, and this repeats for a long duration (could be as little as a quarter or sometimes years) this can deprive the person from any hope that things will get better.
This can also be an issue when your company is growing very quickly. Because there will always be more work that needs to be done, urgent customer inquiries, people issues popping up, you will feel like no matter how hard you swim, you are always sinking or staying in the same spot. This can become worse when combined with loss of [[Intrinsic Motivation]] — if people feel that they are loosing more autonomy.
People needs to "feel" that things do get better, through hiring, changes in leadership, new process, changing roles & responsibilities quickly to rebuild the hope again, but if this lasts for a quarter or more, productivity and emotional engagement will go down noticeably.
Lacking sense of progress
The Power of Small Wins shows the importance of "sense of progress". When people feel they are stuck for a relatively long period of time, and they feel the environment/team is not really supporting such progress, then it becomes quite demotivating to stay in that role/company.
Make sure as a leader, to continue to recognize and celebrate the progress. It's surprising how much celebrating 'artificial' milestones brings meaning and joy to the team.
Losing balance of physical / mental wellness
This really is a hygiene factor and when is missing, you go all the way down on the Maslow's pyramid. When we are in situation grasping for pure survival and sustainable well being, whether physical or mental, our executive brain (pre-frontal cortex) becomes less active and our limbic system takes over.
The world becomes more black-and-white and we really can't focus beyond the immediate survival and recovery. Make sure your team/co-founder is in a sustainable setting, or they will roll back to this dark state.