I didn't realize he'd mentioned public transit anywhere in the post. I believe he said he intends to get anywhere he needs to go using only "determination and what I ate for breakfast"... I'm no mechanic but I don't think a bus can run on that
if entire cities were designed around these instead of cars...
The only reason you can't live the majority of your life within that radius is because it was designed otherwise. The vast majority of human society has been within 15 mile radii, and many parts of the world still are that way.
European here. Most of what I need are within 2 miles, so for most things everyday I ride a bike. For things further away, there's great public transportation. For when we need to transport bigger things or go where it's hard to go by public transport, we do have a car. However, the car gets used at most once per week.
We wouldn't strictly need a car either. There's several car pools around where you can book a car for a few hours when you need it.
Non european here, the only reason I don't have a bike is because of space and hassle (have a tiny apartment with no garage), I could and would do my commute and most errands on bike, it would even be easier and faster.
I can do 90% of my life within 35km of my house, except occasionally work and visiting friends and the occasional hobby. So I can easily do 9 out of 10 trips on a bike
Just because you use a bike once does not mean you are forbidden from using cars. If you have to go further, you can still take a shared/rented car or your own, if noone lives around you.