I started running while working at a school where the principal was a runner. We would run 3-4 times a week after work, but he was strong and fast. He encouraged me to sign up for a half marathon, and on the morning of the event I foolishly changed my registration to the marathon, having never run more than 8 miles previously. However, stupid determination helped me finish, even though the principal dropped out of the event half way through.
40 years later I came back to running, when it seemed too dark and wet and dangerous to bike before work for exercise. I discovered I was fast. Since then I have gotten slower but I love the feeling of being in control of my performance. Having a goal event and a smart coach are both a big help to keep me on track.