I try to avoid the temptation with time as a total indicator for what my possibilities are for the marathon. It's the not the best indicator, but it's more how you feel, how you cover the distance and how you are able to do the training afterward.
Guessing what the pitcher is going to throw is 80% of being a successful hitter. The other 20% is just execution.
I think the reason working-class people don't write books is because they are encouraged to believe that only certain people are permitted to write books.