I think this is a very common issue, and I agree with Shamou that it's probably experienced by over 97% of the population.
One thing that I've noticed is:
If I'm extremely/overly excited about something and it's almost all consuming and energizing. I'll get really wrapped up in it, and it will just dominate my life, like almost take it over.
The only thing I can equate this feeling to is like a really big sugar buzz or caffeine high. The problem with this is that it almost always creates a big
crash for me, and I end up de-motivated or deciding to stop.
The activities I found I've actually stuck with are those that do not feel like a sugar high. They feel more like "Slow digesting carbs"
These "slow digesting" feelings are less accompanied by feelings of extreme excitement and all encompassing thoughts, but they have more of a feeling of deep knowing and determination. This feeling causes me to make a
life change, and the actions I need to do in order to accomplish my goal become part of my life, and not just on my daily chore list.
It's hard to describe, but in order to really stick with something it really needs to resonate with me on a deeper, and real level, one that I know will become part of my life.
That being said, I still get excitement out of these types of feelings, but they are not just as fleeting or as intense. They are more manageable and real.
I'm learning to recognize these feelings, and now I often ditch goals/ideas which are accompanied by the "sugar high" excitement.
Maybe searching within yourself and deciding if this is a sustainable, real, and worthwhile goal, before committing to something, could help avoid the crash accompanied by goals that really aren't worth it to you.