Why couldn't Pheidippides have died at 20 miles?
You have to forget your last marathon before you try another. Your mind can't know what's coming.
For the novice runner, I'd say to give yourself at least 2 months of consistently running several times a week at a conversational pace before deciding whether you want to stick with it. Consistency is the most important aspect of training at this point.
You don't run 26 miles at five minutes a mile on good looks and a secret recipe.
Running with others can help get you out when you might otherwise blow it off.
How did I know you ran a 4:30 mile in high school? That's easy. Everyone ran a 4:30 mile in high school.