For me, the most common reasons that make me go back and forth between ideas are:
1. Fear of failure. Often times, I keep going back and forth, i.e. I do not commit to a topic, because I keep weighing out the pros and the cons, which of course is a great thing, but up to a certain point. Sometimes, when I cannot commit, deep down, I am afraid I will fail at it, so I keep flip-flopping. The way to overcome this is to go with my gut, take a risk, and go for it!
2. Maybe I feel that none of the ideas I have come up with is a really great idea that sparks my interest or passion. What I would do is go back to brainstorming until I come up with an idea/approach I am happy with.
3. Maybe I am over doing things, and I just need a break to clear up my thinking. If this is the problem, it helps me to take a break!
It's possible that none of the points I mentioned above apply to your situation. But it's important to think about the reason(s) that stop
you from going for it.
Hope this helps.
Sherif