Imagine you would realize you were doing something for the wrong reasons. Let's say, that something is a job, a personal mission. It felt great at the beginning, and maybe it really was, but it doesn't fulfill you anymore. Perhaps something changed, perhaps you changed. Whatever it is that makes the difference, you just realized that it did.
You have to think about all kinds of stuff. Of course, the matter in itself, but also the avalanche of consequences that follows. For example, things you have invested, like time and energy, ideas and work. All that is out the window. Not for no reason, no. At the time you made certain decisions that resulted in a tangible, solid product.
Now, what if you don't believe in the mission any longer. Or, let's say, the mission is fine, but there was a shift in circumstances that led to a fundamental error. The entire mission is off beat. The team is busy, the expectations high, but the means to deliver are insufficient, the motivation poor. What if at the end of the day, your bill just doesn't add up.