"We are what we repeatedly do.” - Aristotle
There was a time in my life where I was running about six miles a day, nearly every day. I didn’t become that annoying person overnight.
The first time I went out on a run, it was on a track at a community college near my childhood house. The loop was one-quarter mile, so I had to run around it four times to complete a mile. The first time I went out, I couldn’t run around the loop once without stopping. I only ran/walk a mile that day.
Then the next day, I woke up and ran/walk another mile. I slowly progressed, but before I realized it, I could run a mile without stopping. And eventually I could easily run six.