When people say “I can't do that” most of the time, they're actually saying “I can't see myself doing that.” When I started running, a lot of people said they didn't know how I could run so far, or that they could never do that.
When I started, I didn't imagine I'd run marathons. I just started with 1 or 2 mile runs. Those 2-mile runs were hard, and sometimes they still are.
Yet being out on the road gets you up on that hill where you have a better view of your future self. One day I saw myself going farther, and then I went farther.
What do you see yourself doing? What steps can you take to get a better vantage point of where you could be? Little steps is all it takes.