Hype gets you started. Purpose keeps you going when the hype has moved on to someone else.

Excitement is genuinely useful at the start, when there is nothing to show and no evidence that any of it will work. It also fades, usually right around the point where the work turns repetitive. Whatever replaces it has to be a reason that holds up on a boring Tuesday, which is a different kind of thing.

Write down why you started, in plain words, while you still feel it. Keep it somewhere you will find it in four months. On the flat days, do the work first and read the reason afterward.