Don’t ever doubt yourself. If you want something bad enough, you can have it. Many of our runners thought they would never be able to run 60 seconds, much less 4 miles. Well, look at you now! Running 4 miles and although it may not be a walk in the park, you’re doing it and doing it well!
I find this guy quite inspiring. He was not a runner, did not have a “runners body”, was not in good health but he made a decision to turn all of that around and look at him now: