"They can because they think they can." - Virgil
Preach it, Virg.
I recently had a heated discussion with someone about doing. To me, taking action is nearly always the right thing to do. Personal bubbles are meant to be popped, comfort levels expanded, and dreams attained. That typically requires a decision quickly followed by an act.
I want to know what I'm made of; how can I figure that out without constantly challenging myself? Something I've learned: you are always stronger than you think. I'm a capable little girl. I figure that out more and more every day.
My friend Emily decided to do a 5K because it is far out of her realm of possibility. I joined her quest for the same reason. Before starting to train, I didn't even have a pair of intact tennis shoes. Now I will gladly talk with you about intervals, stretches, distance, hills, breathing, and any other running related topic. I feel akin to people I see running. I can't wait to cross my first finish line with my first number on my back and in first place (well that's a complete and utter lie but I wanted to keep the "first" theme going).
Realize you can do whatever you set your mind to early. You'll save a lot of wasted time that way.