Once we are midway into a project, a few months down a job or a couple of weeks down a project, it is easy to fumble. To coast. To not do things with the seriousness that you wanted to, when you started.
But it is the messy middle that makes the stuffing of the sandwich great. Otherwise we are simply chewing cardboard.
What we need to understand is that enthusiasm is a verb. It is an ongoing expression of what you bring to your work.
It turns out, everyone can be superexcited when the work begins. The pros do excellent work even in the messy middle as well as the end, because that is exactly how they become pros. Everything else is a destination to amateur hour.