RT- Starting with Excitement and then Piddling Out

I’m finding it hard to sustain my motivation- for anything. I get excited about something (ex. weight loss, business, etc.), start it and then get bored, unmotivated, find something else to focus on without ever following through. Any suggestions for sustaining my motivation? Initially, I like my reasons for choosing goals but then my brain seems to convince me otherwise and I move onto the next thing. Is this a product of my ADHD or just how the normal brain works? Any suggestions? How do I override my brain and its ways?